is there any program that i could use to take guitar parts off a song...so it would be like a ''backing track''

GoldWave, but you'll have to find a tutorial on how to use it.

You need the master recordings of each individual track for a given song, and even so, you're not likely to find those.

It's nearly impossible to remove sounds from an audio recording without ruining or altering it in an undesirable way.

true words!

Thro VOX made some kind of software using some new technology to alter it, while causing minimal interferance

This won't do it but check this out

http://www.youtube.com/watch?v=jFCjv4_jqAY