My current hard and soft:
Mac G5 dual
M-Audio FireWire Solo
GarageBand
Audacity

I'm not a professional musician and don't intend to be. I just want to start singing and playing guitar Blues on my own as a retirement hobby.
Instead of using loops for the drums and bass backing I would like to use actual recordings of my favorite musicians as karaokes. Is it possible to remove both voice and guitar from a recording? If so how?

Secondary question, a little off topic: I need to buy an electric guitar, not too expensive, possiblly second hand.
As a matter of fact I'll stick to a slow tempo, like Blues does, so I don't need a "fast" guitar. I don't care about the look or the shape since I find them all ugly whether Strato or LesPaul or whatever. I don't care about accessing the highest treble notes.
I care only usability and sound.

What are the specs I should put on my list? Any brand you would recommend?

TIA

Nick