You should be able to go in thru the LINE input. You can record and play back as many tracks as your computer has horse power to handle but with a stock sound card you can only record two (either stereo or dual mono) at a time.
Just use an audio cable with 1/8" stereo pin on one end and RCA (red and White) on the other end. You can pick it up in any radio shack for less than 5 bucks.