It’s been well documented at this point that Lion deactivates the DisplayPort on unofficial 5870 and 5770 cards. (Some 5770s will not run on Lion at all, but some do, including the single slot model.)
Maybe you’ve gone ahead and installed Lion, and are living with the card minus DisplayPort functionality. Or maybe you are holding off on Lion because you depend on DisplayPort for one of your displays.
Hopefully this patch will help. What it does is slightly modify the video driver for these cards, in a way that allows DisplayPort to operate. Unfortunately, only two displays remain operational – in other words, if you have two DVI displays and one DisplayPort display, one of your DVI displays will be knocked offline when you plug in your DisplayPort display.
It’s not a perfect solution. However, this is a working solution for those with one DVI display and one DisplayPort display. (If your only display is DisplayPort, the problem is completing the Lion install itself, as the DisplayPort will be disabled during this process. If you have a back-up video card, you can use that card to install Lion and install the patch.)
Download the 5xxx DisplayPort for Lion Patch here.
Download the patch uninstaller here.