the only way i can think of doing iis to buy some cable that has a headphone jack input and a RCA on the other end. this way u can the headphone jack to the laptop and the rca to the auxilary input of the Head unit.
Like both of the above said. Try mp3car.com. Awsome forum. Check the FAQs before you begin posting. I have my computer run through the Auxilary Input on my Pioneer. Works flawlessly.