Cad/ Cam computer build questions

I'm looking to put together a computer for office multitasking and using very good cad/cam 3D modeling cnc software. I was thinking of a quad core Intel, Asus P5Q Deluxe motherboard, and a WD Raptor HD and XP Pro that I already have. Cad software manufacturer says there are issuses with some higher end Nvidia & ATI cards and recommends a Nvidia 8400gs or a ATI HD 2400 and a min. 2 gigs of ram. I have a $600 budget for cpu,mobo,video card and ram. I'm looking for dependabilty, speed and to keep the noise at a minimum. Any sugestions would be great. Thanks in advance. NO OC or games.