I have a Mac Pro (1,1) from 2006. I just lost my Nvidia 8800 GT graphics card and am looking for a replacement.

Does anyone have any advice on where best to buy a replacement in the UK? I have just seen that I have PCI slot-1 inside my machine. I read that some PCI 2 cards will work backwards - is that right?

Any help would be appreciated. As well as sourcing new cards, I have also looked at Ebay and seen a number of 8800s for sale - are they all going to be compatible with my older machine?