Vista line in distorts sound and wont process stereo

I was just setting up ACID pro on my dell studio laptop, running vista home premium on Intel duo 2.0 ghz, and my line-in distorts sounds from my guitar amp with a lot of background noise and doesn't receive stereo. I am using 2 1/4 cables with a stereo 1/4 to 1/8 converter which worked fine on my old xp machine. My port says it's a microphone/line in, and I've set it to default. My driver is the IDT High Definition Audio Codec which i've read causes a whole ****bag of problems, but I haven't found anyone with necessarily this problem. Everyone else's solution seems to be to roll back to a sigmatel driver, but I don't know if that will solve my specific problem, or where even to get the right one specific to my motherboard. Would it help, and where can I get it?