thers 2 downloadible softwares that i know of....kristal...and reaper. which 1 is better, and how do u run it from an amp to the computer to record?
i use kristal and its pretty good(especially since its free). i just use my effects processor (toneworks AX1500G). you take a guitar cable and put a line in jack over it (you can find these on the end of big headphones, like ones from the 80s). then i stick that on the end of the cable from the processor the the comp(mic input slot) and record.

AnalogMan Stereo Chorus
Barber Tone Press
Way Huge Supa Puss
I think Reaper is a lot better. Just consider that it is still under development and updates are posted regularly. Kristal is no longer supported I think (or at least updated). And Kristal cannot handle midi, soundfonts and all that jazz.

The easiest way to run your amp into the computer would be via a microphone plugged into the line in jack of your sound card. Or you could buy an interface (Line 6 Toneport) and forget about the amp.

Good luck!