in the start menu, choose programs, then accessories, then choose entertainment, the click on sound recorder...
once you open it choose edit, then sound/audio properties, and you can select where you record from be it the line in, or mic in....
use line in if you can, youll need a Y-cable though, which has left and right on one end to connect to the output of your stereo, and a single 1/8 inch jack on the other which goes into the line in of your soundcard