First time poster, long time lurker. I just picked up a 2006 Mac Pro 1,1 last week for a great price ($150!!) it's fully functional and updated to 10.7.5, 16GB RAM, 2x2.66 quad. I got it planning to upgrade to Yos. or Cap. so I could run Logic Pro X, etc in my home studio workspace. Bought an XFX HD 5770 from eBay, the seller claimed it worked with Mac, but I should have been wary when he said he only had a molex to 6 pin connector. Got the card today and have tried just about everything I could think of to test it's viability to no avail. I tried both DVI ports, DVI to VGA, even HDMI...not a flicker. I'v spent the past couple hours coming the boards and haven't been able to find anything definitive re: whether it will work or not. But at this point I'm thinking no. Posting this thread as a last hope. I've contacted the seller about a return, but nothing yet. Any one use this card successfully? The price was right compared to the others on offer and I jumped at it, this being my forst go-round with Mac Pro, although I'm a mac user since the early 90s and pretty handy with computers in general. Thanks in advance.