"the volume levels on the recorded audio keep going up and down."
Find out how to disable AGC on the card's sound control panel. I can't tell you where this is since there is no standard place for it. Here's an article about AGC and sound cards.
I have connected my decks up to my pc via a mixer in a view to record my mixes to burn to cd but i'm having problems. I have an RCA-1/8" cable running from the out on the mixer to the line in on the soundcard and although I can record what's being played, the outcome isn't great. Basically the volume levels on the recorded audio keep going up and down. I have tried using the microphone input aswell and the same thing happens. Can anyone help? I'm using Win XP build on a P4 3.2Ghz 512mb ram with asrock motherboard. The soundcard is built into the motherboard and think it's AC97 or something like that!