I dunno if you can hook your stereo speakers directly to your PC, however, you can use a stereo with an AUX port to transfer your computer sound to your stereo.
what kind of speakers are they .. you need a 3.5 jack to Red/white cables - thats what i used until i bought proper PC speakers http://www.amazon.co.uk/Belkin-3-5mm-Jack-...e/dp/B0002AFT7M
Yep, you should use a Stereo or a seperate amplifier, if you use em without, you wont hear much. Easiest way is what Shock discribed, try that.