Yes, I think you're out of luck. You are referring to "tracks" as they are in the early part of the recording process with the various vocals and instruments on separate but synchronized tracks. Once it's mixed, they're all mushed together and that's what you have on a CD or .mp3 file that you are trying to edit in WavePad. Kind of like trying to remove the eggs from the cookie dough AFTER it's been mixed. Much easier to leave it out if you know about it before the mixing happens. The techniques nchda was suggesting are, as he said, not easy and don't give very satisfying results.
Might have better luck contacting the recording artist and asking if they ever made a "minus-one" (karaoke) version of the CD.
Bob Hickling in Princeville, HI