I've got a dual G5 with 1.5 GB memory, and I haven't had any problems with P5 being slow... the only time I notice problems is if I've loaded TONS of textures in one file that aren't being used, but closing P5 and reopening it fixes that. Have you installed SR4? And I assume you're running OSX 10.3.4?

Keep in mind that Poser 5 CANNOT take advantage of dual processors... so you'd be getting the same optimal speeds on a single processor machine. But you still shouldn't be experiencing huge delays, I use P5 exclusively and would never go back to dumpy old P4 in classic.

~ Molly