Hi. I'm into digital recording. The best program i suggest for this purpose is called Cubase. Nice little recording program. Or Cakewalk 9. your choice. Cake walk is more for MIDI recording where as Cubase is fully audio.
Now to get the sound into your system: Unless you have a recording card, or a serious sound card, there is no real way to do this. unless you go through the mic input. which should not be too bad mind you.
I got myself a Gadgetlabs Wavepro Recording card. Very Nice. Direct input into the pc from the sound system. but they a bit much on cash.
As for hooking it up: There should be an aux out on your system, or a head phone out. plus a plug into here, and into the back of your pc. simple as that. Not sure how the quality is gonna be though. But if its cassets or LP's you backing up, I'm sure quality wont be much of an issue. you still gonna get that annoying static in the background sadly.
But I hope this helps. Give a shout if you need help. hotmail is:
morneoos@hotmail.com
Later bro