Audio samples for a song! help please!

There are a few different ways you can go about getting rap vocal tracks aka acapellas.

1. Search Limewire/Torrents for Acapellas and see what turns out. ie: 'biggie acapella / rap acapella / acapella  etc.

2.
http://www.rapapella.com/


3.  Vinyl.  many times the record label will have an instrumental track and a seperated vocal track on vinyl records. Look for the vinyl singles of the the track you are looking for and this could be the case.

They did this for djs

4. You can try using audio programs to extract the vocal channels out of the track, since the vocals are generally mixed down into the center channels of the track. Similarly in audio programs you can take an instrumental version of the song (just the beat), stack it up against the actual version of the song you want to take the vocals from.. and  then select the complete inverse of the track.. which in a perfect world would just be the vocals.
Reality of it is though that what ever you get left with.. even after much polishing is generally going to be a dirty sample. It'll pick up on other noises, frequencies, and channels.
I really don't suggest wasting your time on this technique or programs that claim to do it for you as it's going to leave you dissapointed.