We don't have RhinoCam, but we do have 21 seats of Rhino installed on a variety of computers (from 8 years old to brand new). As system administrator I am directly involved in the installation, and my experience tells me to stay away from ATI cards. NVidia cards work well 100% of the time, but with ATI there is a lot of monkeying around with drivers (some older ones are better than the new ones) and with settings. If you get the ATI card to work well, then it does wrok well. It's the process of getting there that is aggravating.
As for processors, get as fast a processor as you can afford, but don't worry if you don't have the absolute latest. Rhino is not that demanding. I would go with 2Gb of RAM though. Don't skimp out there.
I'm running on a 3 year old P4 3.0Ghz machine with an older Nvidia Quadro 980XGL with 2Gb or ram. I have worked with 650Mb files without any problems, other than being a bit slow.
Maybe someone with RhinoCam can add any specific requirements of that product.
Hope this helps,