You can go down to your local electronics store and buy a cable that does this. It will seperate the mini-stereo jack to dual rca cables that will attach to any home stereo system that have rca cable in jacks. The cable should cost you less than 10 bucks. I did this before to play games on my home theater systems 440w amp. Makes for an interesting gaming experience, especially if you have good tv out and can hook your sytem up to your tv and stereo.
Nope, this is full stereo output. The mini-jack is stereo, the splitter cable you buy must also be stereo. The splitter cable then just splits the cable to left and right rca jack channels, so you will get full stereo sound from this.
Another cool thing, if you have a home theater system, is alot of games (such as unreal) have native dolby prologic sound encoded. Your sound card does not need to be able to decode it (with most programs), because it just sends it out to the reciever for it to be decoded, just like your hi-fi vcr does. This way, if the games you are running support it, you can get really cool 3d sound without having a 3d sound card.