Your laptop should have a 'line out' socket, or if not (like mine) then it will definitely have a headphone socket, plug a '3.5mm mini jack to phono' cable (see ebay link below) from that laptop socket into the 'line in' socket on your stereo and jobs a goodun
Bad news is that most cheap stereos dont have 'line in' phono sockets. A lot of expensive ones dont either
The type of cable I use...
eBay.co.uk: 1.2 M 3.5MM MINI JACK TO 2RCA PHONO CABLE LEAD (item 280092235830 end time 13-Mar-07 00:54:25 GMT)
You will also need to switch your stereo setting from either radio or CD (the usual settings) to the video/aux setting so the sound from your laptop will play