Unlinke many 3D applications, Rhinoceros 3D is designed to work on an ordinary PC. However, here are a few recommendations:

• If you're running with less than 128 megs RAM, adding more will help your performace more than anything else
• There are no known problems with Rhino and AMD Athlon processors, nor any particular version of Windows
• I won't speak for anything other than Rhino, but I use and recommend Nvidia-based video cards