Removing instrumentals from song?

Some DJs can only get the vocals, how do they do that?

They're called Acapellas. They are versions of the songs that contain only vocals. Some acapellas are online and you can download them through limewire. But if you're into mixing, you have to get the vinyls. Most vinyls have singles in both radio version, accapela, and intrumental so mixing is easy.

Good luck.