Well, this isn't a general hardware question, but as long as the topic's unlocked and I'm here typing anyway...
One simple way to do it is to open a recording application, I prefer CoolEdit, but whatever you have that can record long wav files in full 44.1/16/st. Either through the app or through the Windows mixer directly change your recording device from the default of microphone to 'stereomixer' or 'what you hear'....depending on soundcard the devices are labeled differently someimtes. Set your levels, hit record, come back in 2 hours (or how ever long the show is) and save the wav. For CDs, break it up by the hour.
Best bet is to turn off windows sounds and close ICQ/AIM/ETC especially if you're not going to be sitting there listening anyway. Since you're recording the sound mix that's going to your speakers you'll also get windows system sounds...all the beeps, boings, chings that occur. If you just have the recording application running, no problem.