if your using the sound recorder i used, which is the one that came with vista, dont. i tried using it and it sounded like absolute crap. i had so much static and background noise that i could barely hear what i was doing. i would suggest downloading some free recording software that will get the job done, and if you can find it, get like a converter or something like that so you dont have to go through the mic plug-in.
if your dedicated to recording yourself then you can do what i did. i ended up getting a mixer and ran it through that and ran the stereo outputs from the mixer to the usb port on my computer and it sounds absolutely amazing, you can just get a cheap mixer, mine was about $150 but that was because i needed something with i tiny bit of balls but you can get smaller ones if need be..
like i said, if your dedicated to it, or have more of a reason then just for the hell of it, i would say go for the mixer route.. if not.. then sorry