If you go to Kalm after Meteor is summoned, the old man there will now give you a quest: find 3 tems for him, so that hey can continue his journey. These items are: The Guidebook, The Desert Rose, and The Earth Harp. This walkthrough will tell you how to obtain each of them.
The Guidebook
Down in in the tunnel in front of the entrance to the Underwater reactor in Junon, there is an enemy called Ghost Ship. If you morph this guy, you'll receive the Guidebook as your reward. Take the book back to the man in Kalm, and you'll receive the Underwater materia, which will become important in the next battle.
The Earth Harp
To get the earth Harp, you'll have to defeat an enemy. Unfortuanlty, he's a little bit harder than the Ghost Ship. Quite a bit harder, actually. The Earth Harp is held by Emerald Weapon, down at the bottem of the sea. The only way to get it is to destroy him. With a little bit of planning, though, this should be easy enough.
I've defeated Emerald several times, and I found that a party made up of Cloud, Yuffie, and Barret works the best. I had my people equiped something like this:
Cloud: Ultimate sword, Escort Guard, and a Ribbon.
Yuffie: Conformer, Minerva Band, and a Ribbon.
Barret: Missing Score, Imperial Guard, and a Touph Ring.
For materia, I gave them these.
Cloud: 2-3 mastered HP Pluses, 1 Mastered MP Plus, Knights paired with MP Turbo, Underwater, and a Mime.
Yuffie: 2-3 mastered HP Pluses, 4x Cut, an enemy skills with White Wind and Big Guard, and a Mime.
Barret: 2-3 mastered HP Pluses, Gravity paired with Quadra Magic, Pheonix paired with Final Attack, and a Mime.
Since you have the Underwater materia equiped, there is no time limit for this battle. Start by having Cloud cast Knights, then have all your other people Mime it as many times as you can. If the chain gets broken, try to have Cloud cast it again. If that isn't possible, have Cloud do normal attacks, have Yuffie use 4x Cut, and have Barret use Demi 3. If Barret get killed, he'll use Pheonix, bringing himself and any other dead charcters bac to full health. With persistance, you should kill Emerald fairly easily. When you win, take the Earth Harp back to the old man. He'll give you a Master Magic, Master Summon, and a Master Command in return.
The Desert Rose
The Desert Rose is held by another, stronger weapon. His name is Ruby, and he lives in the desert surrounding the Golden Saucer. You can see his eye sticking out of the sand. To initiate the battle, just fly the Highwind into it.
I used the same people, with the same equipment. The materia setup was diffrent, though. I only used Cloud for this battle, but you can use whatever character you want. It isn't that important.
Cloud: 2-3 mastered HP Pluses, Knights paired with HP Absorb, W-Summon, 1-2 Mastered MP Pluses, and Master Summon paired with MP Absorb. If you want to beextra cautious, also take along Pheonix paired with Final Attack.
Before you actually go and attack Ruby, get into a normal battle. Have the character you're going to use against Ruby kill off the other 2 people in your party. Now, fly the Highwond into Ruby. He'll imediatly stick is claws in the sand, since the other 2 people are dead. Now, use W-summon to cast Knights on the tentacles behind you, then on Ruby himself. When Knights hits the tentacles, they'll momentarily retract, and Ruby won't be able to hurt you more than once. Because you have HP and MP absorb, your stats will always be maxed out. You should be able to easily beat him using this method. When he's dead, take the Desert Rose back to the old man to receive a Gold Chocobo. However, since it's difficult to beat Ruby without using Knights, you'll probably alrady have a Gold Chocobo.
Here's an alternate method for beating Ruby, which I received from "Khaos."
Right then, before I went into the battle with Ruby, I killed off my other party members, which happened to be Cid and Tifa. I equiped Cloud with his Ultimate Sword, the Imperial Guard and a Ribbon. For the materia, I equiped a Knights of the Round (at level 4) and linked it to magic counter. Than, I equiped a mime and linked it to [command] counter. As for the rest of the materia, I gave him master magic and a master command materia, two mastered HP plus materia, and a W-Summon materia. Now, when I entered battle, I used a hero's drink so every time Ruby attack, I would counter with 2 knights of the round doing 9999 damage. Than, I would mime, which would cast knights or the round 2 more times. I had heard that Ruby was near impossible to beat, but it took me around 15 minutes to take him down.