Graphics for an old workstation, Dell Precision 670

Hi,

I would like to upgrade graphics card of an old workstation, dell precision 670. This is a spare computer in my office and I would like to use it for some gaming and CUDA GPGPU programming.

It has;
Dual 3.00 Ghz Xeon processors on 800 Mhz FSB (with hyperthreading)
2GB 400 Mhz DDR SDRAM (might be DDR2, I don't know)
650W power supply (4x free SATA connectors and 2x free molex)
1 PCI express x16 slot (probably not PCIe 2.0)
and adequate space and air cooling in the case

I was thinking of getting either a nvidia GTX260 or GTX285 but I am not sure if these cards work with this PC. I know these cards are far too fast for this computer but this is just temporary. I will buy a new PC after a few months and use this card in it. I just want to know if I have enough power connections and if the PCIe 1.x version is compatible with the newest cards.

Thanks in advance

P.S. I know there is a similar thread but I couldn't find my answer in that thread.