Hey, thanks Axe!!

Here's what you need:
- A PC
- An interface to connect your guitar to your PC. Many amps will do this today. I used my Zoom G5 pedal.
- Multitrack recording software. I used Adobe Audition. You can get a copy of this for free now, though it doesn't officially support Windows 8. The install generated some errors, but it works fine.
- A backing track

I downloaded the backing track and loaded it into one of the tracks in Adobe Audition. I then armed a second track to record. The backing track would play as I jammed over it and Adobe Audition would record what I was playing.

Basically, this all turns your PC into a multitrack recorder.

There are other solutions with Tascam pocket studio products and stuff. What I like about the PC solution is I can do a lot of post processing if I want.

Protools may do this for you too - I've never used it.

Hope that helps!