Click Start->Run enter "pbrush.exe" click OK and there you go
oh - that's cold.
There are a bunch out there but you're going to get what you pay for.
Rhino Cad is pretty well respected as a low cost powerful platform
Turbo CAD is decent.
Top players are solidworks and AutoCAD but mucho $$$.
You looking for 2D or 3D modeling?
