One thing that really irks me is some bits of Vista just don't fit on a 800x600 screen in portrait mode.
See how the right side of the dialog is off the screen?
This is just poor design. The minimum supported resolution for Vista is 800x600. Vista includes tablet functionality. Tablet screens rotate.
If you are building Vista apps assume that screen resolutions will vary and make sure they are still readable at 600 wide. Good design would have the above form resize.