Your first problem is the usb can. You need a fw cam (isight) if you want better fps. A video card would help too. Do you have an ata card already? If not, get one, that will help alot-go with Sonnet-those are made by Firmtek and are the best there is. B&W G3's are one of the best computers Apple has put out-save your bucks and keep it a while longer.
-Maestro