We do not use or support vista at my work yet, this is with all xp pro machines...
The problem is, that the video out options do not work as they are suppose to, and they override the application settings. For example, I will set video out in theatre mode (in VLC, WMP, WinDVD, etc) and it will output in windowed mode, and if I do get it to work and if you minimize the application it kills the video out. This will not be a problem when all the classrooms get digital projectors, which will be soon because all video out will be done through them.
Also, ATI's Linux drivers blow compared to Nvidia.
As far as just basic functionality you would never tell the difference until you tried to do some advanced configuration. I for one, on my personal computer, have it working fine with video out to my TV. At work, we have 100s of work stations that do not work properly. They use PCI express Radeon x500 ~ x800 video cards w/ svideo out. They are basic cards, but the only function we need them to have is TV out so the teachers can display videos onto the TVs. It doesn't work like it is suppose to.