S/PDIF Onboard AC'97 Probs

First of all, here are my specs:

Asus A7V8X mobo
AMD Athlon XP 2700+
512 MB DDR 333 RAM
Radeon 9700 Pro
Realtek AC'97 audio with S/PDIF Coax Out
Win XP Pro SP1
Creative Inspire 5.1 Digital 5700 Speakers

I'm a newbie when it comes to sound, and I can't get the S/PDIF out to work with my speakers. I would love to get my surround sound working for both games and DVD's but I haven't the slightest idea how. Right now I'm just getting stereo sound and thats not good enough! Is there a way of getting my onboard sound to work or should I buy a sound card? I'm pretty sure my onboard sound has the ability to give surround sound using S/PDIF but how? If you recommend getting a sound card, which should I get? I've tried going to the properties of the onboard sound and enabling S/PDIF out but it didn't work. Any help would be greatly appreciated. Thank you