Although not free, I must say that the Connectix Virtual Game Station is the Playstation emulator that have impressed me most.
I've played both GT2 and Tekken 3 quite a lot using it, and no problems whatsoever. I've also tried Bleem, and while the option of using filtering/higher res, etc. makes the games look better it's FAR more buggy, Tekken 3 ran like utter cr@p (although rather nice-looking cr@p )
Anyway, there is a demo version of VGS you can download, no timelimit or such, works great. It has some features disabled (no memcard support etc.) but still, if you want to run PSX games it's sure worth a try.
Connectix VGS