Hey guys. Just type rock band multitracks in Google and you will find them very quickly. It's not that difficult.
You will either get ogg, mp3 or wav files or Mogg (MultiOgg).
In the first case, open Audacity and do import and select all the track (for example : Drums, guitar, rythm, song). then mute what you want.
If you have Moggs, open Audacity and do the same thing, import the mogg file. It's one big file with all the tracks in it.
Then you must set some tracks in stereo because they were split in mono. So listen to all the tracks seperatly and when 2 sounds the same, click on the arrow and select "Set to stereo". Be careful with the bass drum and snare, sometimes they must stay mono, cause if you set them stereo you will have kick left and snare right (many songs here on the site have that problem because the idio** who made them weren't careful.
Hope it helped.
If you still have questions, PM.