With a new DX10 ATI driven card here the 7.9 version of the catalyst and drivers were seeing one persistant error as well as seeing the screen go black once the desktop should have appeared. The ATI FaQ and troubleshooting section pointed out the vga port problem.
I ended up still seeing the same on XP when trying both ports until the 7.10 came out. For awhile it was Vista only with that being seen on XP. With the 7.10 the only problem seen now is the Start taskbar being transparent in the portions where there is no acitvity. That would be around the clock and any windows open while the Start button turns the same as the desktop.