I want to put together a workstation but haven't built a computer in years and have no idea what any of the new processors are geared toward. I will mainly be using 3d CAD software (solidworks) which uses OpenGL rendering. Should I go with Xeon, Pentium D, Athlon, Core Duo, etc. Is there any noticeable benefit from building a system with 2 cpu's? Any other advice? Thanks.

Dual core and the latest quad core cpus are best, when the application is designed to use them.

Although applications run just as fast when utilizing only one core.

Current reviews though, have the Core 2 Duos as the fastest cpu for the moment, in single-threaded and multi-threaded applications.

As an example, you can buy a workstation board that allows you to install 2 quad-core cpus, for a total of 8 cores. :D I believe they make a Mac with 8 cores.

Couple this with a lot of RAM, a pair of video cards running SLI or crossfire and RAID 5 storage, and you have one really fast PC. :)

Yeah, yeah, if you got the cashflow (or can scam a client into helping you pay for some of that:D ), that'd be nice. But you don't need all that to do 3d CAD without lag.

A friend of mine is into CAD, and with CPU speeds being what they are, he chose to go for the highest front side bus speed he could find (over chipspeed) which I believe was an AM2 chip architecture, at 2000Mhz FSB. It doesn't QUITE keep up with the CPU, but truly, keep in mind that, like a chain, it's only as good as the weakest link. They're selling dual-core systems with pretty awful (by today's standards) FSB.

For doing CAD on a budget, I would say AMD 64bit will be almost as good as dual-core, at half the price or less. I would definitely look at your FSB, (even on a low budget, I'd say these days don't settle for less than 800Mhz) and I would also make sure that you're getting some PRIMO memory to put in there. I'd rather have 1Gig of GREAT dual channel memory than 2 gigs of average memory. DDR2 is faster, naturally, than DDR, but if you do make sure that you have dual-channel memory, and a mobo that supports it, I don't know that the difference is noticeable. Either will blow away a traditional single-channel memory setup.

Same with video. You know you want something nice, the question is just how much can you afford? You can go to ati.amd.com and get a great pair of Crossfire cards for $700, but you could do CAD just fine without something like that. In general, yeah SLI/Crossfire is great, but I'd rather have a top-shelf single card vs two lower end SLI cards. It's all according to budget.