It requires a Pentium 4 due to the SSE2 instruction set, I THINK (I could be off on this) SSF Alpha R3 or R4 and below did not require the SSE2 instruction set but running that was alot slower (I noticed that when he seemed to implement SSE2 the emulator got a significant speed boost).

I should also mention the emulator (as Saturn is complicated) does not use 3D acceleration, and everything relies on your core CPU speed as Roushi said. My setup is 3.4 Ghz Pentium 4, so I was able to squeeze out good speed. It is getting better though, and the guy behind it constantly updates it ever few weeks, so hopefully it'll run on more setups in the future.