If you need a new card, the Apple-firmware 5770 works in all models of the Mac Pro, just not as fast in the older models. Apple does not recommend it for the older models, because by the time it was released, the older models were all retired.
It runs US$250 and will be faster than the 8800. Drivers are in 10.6.5 and later.
Executive summary: If they want more than US$250 to replace your 8800, the 5770 is a better deal.
I'm back. Got my Mac Pro back from repair today. Ahhh...25" screen. However, they (the Apple Repair People) have put a new GeForce 8800GT in, to replace the old one.
And the final bill was $380 CDN ($40 for work, the rest for the card, around $300.)
What's Apple's policy on graphics card replacement, even if the customer is paying for it? I thought I asked for a new ATI 5770 card, but maybe I was wrong. I don't think I can take her back in and ask 'em to put a better card in there, and only ask for a bit more to cover the difference in price. I've got a feeling it doesn't work like that.....