My machine at home is an Apple Power Mac G5 2ghz dual processor running OSX 10.4, with 1.5gb of RAM, 2 x 160gb hard drives, and an ATI Radeon 9600 GPU.
I will be upgrading shortly with another 2gb of RAM, and possibly an ATI X800 card, although this card is quite expensive for Mac. I may upgrade the whole machine later when the new Mac Pro's are released. Yum...
The renders you see here took between 1 minute (the bodywork) to 1 hour (for the closeup of the wheel). I set one render going overnight when I had too many settings turned on, and it took 9 hours. This could have been done in less than an hour, but I had only just got the program, and was a bit over-enthusiastic with my setup.