I didn't see any post similar to this as a solution (nor did i read all 12 pages) but i figured i would throw it out there. I am running:
AMD Phenom II x4 955
4gig DDR3 Ram
Asus M4A78TD-V Evo
Xfx Radeon HD 5670
Every time i tried to install ubuntu 10.04.1 64bit, through Wubi or other, i was having the same black screen problems. I decided to pull the video card (which is only DVI/HDMI, no VGA support) out and attach my monitor to the on-board VGA. After doing so i was able to load ubuntu and finish installation. Afterword i installed the suggested ATI graphics driver (the proprietary one) and restarted computer. After restart i shut down and reinstalled the video card, booted just fine. I am yet to have any issues or to have used it much, other than to do updates and jump on the net for a bit. Going to look into the capabilities of the card with the driver as well as try to force some bugs out of the wood work. I installed it via Wubi on a 17g partition in Win7 64 bit and am testing to make sure it will work fully before i buy a second HD to toss in and dual boot.