I presume the two connectors you are thinking of would be RCA Phono jacks/plugs. The socket on your computer is probably a stereo mini-jack type. The cable you need looks like this:-

http://www.majadu.co.uk/35mm-stereo-mini-jack-to-twin-rca-phono-cable-lead---015m-15cm-299-p.asp (different lengths of lead available)

Or if you already have phono leads providing output from your stereo, an adapter might do the job:-

http://www.dv247.com/pa-systems-and-live-sound/stagg-twin-female-phono-rca-to-stereo-mini-jack-adaptor-2-pack--92286

Shop around - these things can be had very cheap, or you can go to the big electrical retailers and pay serious money.

Ross