lots of ways really, just depends on how good a sound you want to get and how much time you want to spend doing it.
easiest way is you could plug direct from the headphone jack of your amp into your soundcard input (not the mic as the levels will be far too much)
Or you could hook up a mic to the amp and run that into your amp.
depends on the sound, but if you not fussed then just use media recorder as standard on windows...
plenty of other software stuff out there, i used to use sony vegas i think, you can do multitracking with that.
also, possibly an obvious thing to say, but you will need to go into your soundcard properties and make sure you have the correct device selected for recording.
