depends - some pc 5.1 sets come with a wire with 3.5mm green ends (goes in the green hole in the back of your pc). with that it's a simple matter of just plugging it into your earphone port - however you'll only get stereo sound and not the full monty
http://www.hardwaregeeks.com/reviews/steel...tionsremote.jpghowever, the ones with the coloured connectors (for the pc) have the same 3.5mm that each go into the colour coded ports in the back of your 5.1 sound card - those connectors will not fit in dvd systems (the ones for dvd systems look like component leads)
if you're looking to buy a pc 5.1 system for your dvd system, it will not work properly. it may work the other way around (dvd 5.1 for pc) but again the connector pins are too short to fit in the plugs properly and you won't get a proper fit.
hope that clears things up a little