I'm getting the vista black screen as well.
My twist: Everything worked fine with compatibility (I tried all the fixes, and they worked previously).
Then I removed the DX10 card, and installed a DX9 card (GeForce 6200 turbocache). Vista is fine with it, but DDO and other games give me a black screen on load.
I'm assuming the issue is that everything is trying to use DX10, and the card doesn't support it? Anyone have thoughts on how to fix it? I tried compatibility fixes, which you'd think would work, but no good....