I had the Samsung epic 4g (Sprint version of the original Galaxy S) and rooted/installed a handfull of custom roms.
I usually start with XDA forums, specifically for your phone, by clicking
here. But, yeah, there are already a couple of really great sources posted.
Do it, you won't regret it. You can undo whatever you end up doing usually.
Also, always check out youtube. Tons of great info there.