I have a p4 1.8 w/512m 64m video card on old machine and limited harddrive for paging mem - so bought a new machine with tons of harddrive [P4 2.8 intel] w/1g mem 128m video card and the difference in High Detail Rendering is night and day - the difference in standard default rendering is just seconds.

Lots of memory and free harddisk is imperative on any 3d program so far as I can tell. I have purchased many machines from http://www.cyberpowerpc.com and other than being greedy and NOT getting an intel motherboard (wanted to overclock - switched to intel mb!) to go with intel chip - have not had any problem and their prices are pretty darn good....

Good luck moving to pc - I know my best friend finally made the move and the first few months were continual headache for her ('specially when she found her mac software wouldnt work on pc) but now she wont move from pc and she is a college prof in liberal arts arena [artist]- so being pc bound isn't 2 bad ;-)