Anssi, I think Thom mentioned earlier in the thread that SketchUp requires more CPU power than GPU. I think this is true. Bus speed to the processor is also important, I think? My HP workstation I've had to stop using, despite it having an Nvidia 512mb card, It was a P4 (single core- XP 32bit), but ran at 3gHz or something. I've swapped to this Macbook Pro, which although is 3 years old, has a higher bus speed, and is dual-core. The GPU is an ATI X1600 with 128mb vram, and the performance is better (but is now beginning to show cracks!)
I do need a faster machine. Mac or PC, I would prefer another Mac, but it's what gets the job done for the minimum price. But then again, I've had 3 PC's go wrong on me over the last 4 years, but this (Apple) laptop is still going strong! So what's the cheapest now? Do I blow Β£2000 on a new Mac, or Β£700 on a PC that may go wrong again??