Both of those cards are PCI Express and I need just PCI. I definitely want to go with a least expensive option that will work for my setup. The computer has a 128MB ATI Radeon X600 SE now which works well enough. The monitor I want to use has both VGA and DVI outputs. I was thinking maybe 256MB ATI x600 w/ dual VGA or DVI. Will that work well with c3d 2008?
Another quick question - Does PCIe mean PCI Express? I am finding conflicting answers on the internet and I don't want to order a card that does not work since I will be putting it in by myself and am very new at it.
Your entire setup is so painful, though... Rather than try to improve a nearly-dead system, I think you'd be far better served by just getting a new i3-2120 with midrange GeForce capable of driving two large monitors, 8GB RAM, Win 7 x64, all for under $1000. That would save you so much time and pain, from a user's point of view, that you'd make back the cost in time savings before too long.
The other big improvement would also be to get off of C3D 2008. We used it when it was the latest version, but in retrospect, it wasn't ready to be used in production. WAY too many problems. Dealing with all the problems ate up so much time that it was not much better than Land Desktop. There are also sundry problems involved with bringing files forward versions, and the older your drawings, the more problems you'll have when you finally do move to newer software. The sooner you can get on C3D 2011 or 2012, the better.