i'd send that Mac Pro back if you can and get the Quad-Core(8 cpu's) in a few months..
"Mac Pro Octo-Core. For when you absolutely, positively have to sequence the entire human genome before lunch." - Mac Daily News
Yeah, but you know, if I did that I'd never get a new machine because I'd always be waiting for the next thing.
I buy a new desktop machine every 4 years, and I try to do it on a regular schedule. It was pretty well timed this time because the Mac Pro had just come out. I didn't want to buy a G5 since they were getting long in the tooth.