The computer will not amplify, in the same way that a DVD player with on board decoder won't. You can get the computer to decode the signal - you'll need the right version of WinDVD, PowerDVD or other software DVD player.
You then need either a multichannel amplifier and "normal" hifi speakers - this is the most expensive but best quality route - or some "active" speakers - i.e. speakers with amp built in. There are lots of sets designed to plug straight in to your SB5.1. Creative make some, as do plenty of other manufacturers.
Here's an example - not recommending them in particular, but you'll get the idea.
It depends if you're looking for "ultimate quality", or a cheap way to watch DVDs with surround sound from your PC.
