I'm running windows XP home edition, and have had no problems, and I have everything including the kitchen sink installed into poser! lol I do have a 1 gig hard drive though.

Poser 9 SR3  and 8 sr3
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Processor Type:  AMD Phenom II 830 Quad-Core
2.80GHz, 4000MHz System Bus, 2MB L2 Cache + 6MB Shared L3 Cache
Hard Drive Size:  1TB
Processor - Clock Speed:  2.8 GHz
Operating System:  Windows 7 Home Premium 64-bit 
Graphics Type:  ATI Radeon HD 4200
•ATI Radeon HD 4200 integrated graphics 
System Ram:  8GB