This is a fairly easy thing to do. The hardest part is finding your song.
Code for MP3s
Code for MIDIS
When you find the song you want, right click on the link and click "copy shortcut." Paste this in the code where it says "SONG URL." You MUST leave the quotations if you want it to work. Paste the entire code somewhere near the bottom of your page, so it's out of the way. You can adjust the dimensions of the box to be more than 25, but not less because it won't work. Right clicking the box will give you options to stop the music. Do not use on Expage.
This is a great place to get MP3s. They have any song you could ever want. A lot of their songs are about 30 seconds long, so if you want a full-length one, look carefully.
I really have not found a better place for MIDIS than than here. They have quite a few songs, but most of the ones they have are from really famous bands and singers.