The Wood Elves generally have an easier time handling their dark brethren than the High Elves do (hatred is never fun to deal with), but Dark Elves are still one of the most challenging armies for the "Good Elves" to fight against; a Wood Elven general cannot exploit the elven racial advantages (very good maneuverability, great missile troops, great initiative, good leadership) as he can with other races. On the other hand, Dark Elves suffer our same racial disadvantages: low strength, low toughness, and high point cost.
Although differences between the armies are finer, they still exist. The Dark Elven advantages:
1) Better cavalry. Cold One Riders will mow down even heavily armored Glade Riders; the two S4 attacks from the Cold One combined with a 2+ save will overwhelm any Wood Elf Cav. Dark Riders, with their expert riding abilities, repeater crossbows, fire and flee reaction, and free march moves are much more dangerous than missile-armed Glade Riders; they can get 12-14 close-range shots against valuable troops before you've even moved!
2) Dark Elves rule the skies because point-for-point, and maybe even in a straight-up comparison, Harpies are better than Warhawk Riders. At only 15 points apiece, the Dark Elf general can get two Harpies for every one of your Warhawk Riders . . . before you equip them. Harpies have S4 T4 and two wounds in addition to their possible rank bonus. The thought of "glancing blows" against Warhawks by a big Harpy unit flying high makes me cringe. The saving grace: Harpies have terrible leadership and no armor save. The Wood Elves can exploit this on the battlefield, but can't expect to challenge the Dark Elves up high without a disproportionate investment of points.
3) Dark Elves have incredibly cheap scouts. At 13 points a model, Dark Elf Scouts cost the same as a regular crossbowelf with (the required) light armor. An opponent unworried by army composition concerns could easily have three or four good-sized units of BS 5, two-shot scouts starting the game uncomfortably close to your deployment zone.
4) Witch Elves. If these scantily-clad ladies engage any unit in hand-to-hand combat (save a Treeman), it's going down. Even Wardancers. Those 3 S4 attacks are Nasty with a capital N, and the unit apparently comes factory standard with a tooled-up Witch Elf Hero. True, they are extremely vulnerable to missile fire, but the Dark Elf general has plentiful scouts (see #3 above) to provide screens and cheap aerial units (see #2 above) to engage any of your archer units on hills. Witch Elves are -the- primary target for the Hail of Doom Arrow, in my humble opinion.
The Wood Elven advantages:
1) Missile Range. Wood Elves have an incredible 12" range advantage over the Dark Elves' repeating crossbows. This is not as big an advantage as it could be considering the cheap Dark Elf Scouts, but with proper terrain placement you can do a lot to preserve this advantage. Definitely set your Archers up in the -back- of your deployment zone if at all possible.
2) No big RBT targets. Wood Elves don't have a lot of units with big ranks or armor, so a Dark Elf reliance on RBT's is not as well-placed as it would be against, say, Empire or Chaos. There's not a whole lot to shoot at and a lot of what there is is skirmished. In addition, Wood Elf archery can make life very "exciting" for RBT crews.
3) Waywatchers. Waywatchers are one of the few scouting units who can take on the Dark Elf Scouts successfully . . . the Waywatcher special abilities outstrip even the power of the mighty repeater crossbow.
4) Dryads. Dryads will carve up most Dark Elven units (save Witch Elves). "Willow Aspect" strikes fear in the hearts of even Cold One Riders.
5) Treemen. The Dark Elves don't have anything in their army list that can really match up with a Treeman outside of a very large monster (read Manticore or Dragon) or a tricked-out general.
Unit: Recommendation (z x n). Analysis. Where n is the recommended number of troopers and z is the recommended number of units (if no z then one unit recommended)
Chariots: No. They are far too vulnerable to missile fire and aren't fast or maneuverable enough to escape the Dark Riders, Scouts, and Harpies. Leave them at home.
Glade Riders: Yes (1/2 x 6/7). Glade Riders are an instrumental part of any Wood Elf Army, in my opinion. Give them light armor and shields, skirmish them and go after the Dark Riders. You might want two units (one to hunt Dark Riders and one to flank ranked enemy) but that is normally prohibitively expensive.
Warhawk Riders: Maybe (5/6). They can never fly high because of the Harpies (see above) and will therefore get charged by a ranked unit of Harpies on turn two. They can win this battle but only if they have a hero or the general in the unit (a champion with the Shrieking Blade works sometimes, too). If you want to make your Warhawks your big hammer unit, then okay. Otherwise leave them at home. Remember that they're skirmished so they can't test off the hero's or general's leadership.
Wardancers (6/7): Maybe. A perennial favorite, Wardancers do well against all but the most heavily armored/high toughness foes, and even then can give a good account of themselves if you take a Champion with the Potion of Strength. However, Wardancers are extremely vulnerable to missile fire. Three guesses what a Dark Elf army has.
Archers: Yes (18+). Is it a Wood Elf Army? It has at least two units of nine archers. End of discussion. ;-)
Waywatchers: Definitely (6) (see above).
Scouts: (2/3 x 5) You can't afford to be out-scouted by the Dark Elves. Take two or three units of five scouts; give at least one a champion with a cheap magic weapon.
Treeman: Yes (1) (see above), if you have the points. If you want a Treeman you probably can't take Warhawks.
Dryads: Yes (5) (see above).
Magic: If you go wild with magic (Lvl 4 mage with appropriate accoutrements) you won't have enough troops to do the job, in my opinion. Go with the Lvl 2 mage, Rod of Power, Skull Staff and stick him in a wood within 12" of an archer unit with the Banner of Sorcery. Most Dark Magic spells are fairly high power cost, so you should have a good shot at shutting down his magic phase for a minimal (around 210 point) investment.
Unlike most games, you probably want a wide open "kill zone" in the middle of the field with as few pieces of terrain as possible. You want to minimize the Dark Elves' opportunity to deploy his Scouts close to your deployment zone, so most of your terrain should either be in your deployment zone or as far away from it as you can get. All but one forest should go in your deployment zone so you can hide units from Harpies (no flying into the woods) and Dark Riders (if you can't see it you can't shoot it).
It's very important to deploy your vulnerable units (Warhawks and Wardancers) where a first turn Dark Rider volley won't cause unacceptable casualties. This means deploying 2" back in the woods or behind some big piece of terrain in your deployment zone.
Wood Elf units operate best in teams, so create them in your mind while you're making the army and deploy the teams together. Sample assault teams: a fast assault team with Treeman (frontal assault) and Glade Riders (flank assault); a "stick" assault team with Wardancers (frontal assault) and Dryads (flank assault); a -very- fast assault team with Warhawks (+general) (frontal assault) and Glade Riders (flank assault); you get the picture. It's very important not to put units out on their own; the Wood Elves depend upon units supporting each other.
It's also important to give each team a mission. Scout teams should dispose of enemy scouts, assault teams should take on main enemy units, and some fast assault teams can try to break through the lines and rampage through enemy missile units (although the Dark Elves can't hold back many of their missile units except RBTs because of the short range). Against Dark Elves I would assign one Scout team (Scout unit w/champion + Waywatchers) to Scout hunting and another (with one or two Scout units) to RBT hunting. This frees up your fast assault teams to hunt down more worthwhile enemy formations.
Punish Witch Elves with as much missile fire as you can muster. This will normally mean pulverizing a screening unit on Turn 1 but there you go. Take advantage of their frenzy if they pass too close to a Waywatcher-infested forest; traps take a terrible toll on these deadly damsels. Definitely do -not- engage them in hand-to-hand combat if you can avoid it; it's just too bloody.
An assault team of Dryads + any other unit can deal with the Cold One Riders. Willow Aspect is the key. If you can't set the Dryad team up opposite the Cold Ones for some reason then send your Treeman team after them.
Your mage should -never- leave the comfort of the forest; it's just too dangerous out there! :-)
Please write (firstname.lastname@example.org) and tell me how these suggestions worked or if you have questions or comments this post didn't cover.