Quote - Having the same Mac and Video card as you, there aren't many options available. Apple doesn't give us many options for an upgrade. PCI Express 2 will work in PCI Express 1 just not supported by Apple. I finally bit the bullet and bought a ATI Radeon HD 4890 pc card for my Mac. It works great and it supports Open GL 2.1 Shader 4. Vue is much more stable with the newer card. The whole pc card to Mac can seem complicated but it works and can be done. I can post more if your interested. 

Thanks for the info danway. I've been eyeballing the pre-flashed ones on eBay, though some of the guys on the Apple forums seem to have no issue with doing it themselves and who knows, maybe it's cheaper that way? Was yours an off the shelf PC model or ...?