Does any one know of equipment or computer software that isolates and eliminates the guitar in mp3 song files so that I can plug in and play the lead instead?
Just look up backing tracks for the songs. They should eliminate the lead parts for you. And as for Original recordings, just mute the lead guitar part!

I don't really think there's any software that eliminates parts, but I could be wrong
Adobe Audition had a vocal remover that could be adjusted to take out vocals. May be able to adjust it to take out guitars.
I'm hungry.
removing tracks from mastered music is not exactly a science. all the overlaying frequencies make it impossible to cleanly remove a track by just EQing it out so there is some software and hardware that use some tricks to make the guitars less prominent

the backing tracks idea is better, may not sound exactly like the album, but some of them are pretty damn good.

another option is midi tracks, you can get free software like powertab that has quite a few more popular (and quite a few less popular) songs arranged in midi.

you could also record your own music and solo over that.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
^^ Exactly how i roll^^ haha - I usually look up the tabs for guitar pro that have the drum parts in em and then drop that midi into superior drummer and track over that..
at one point or another i could've sworn i downloaded an app for my mac that pulled apart the different parts of a track but i can't find it and don't remember what it was called