XP is simple, Home or Professional. Most people could get the home edition and never know the difference. At school, we needed the additional features of Professional. No big deal, everything in the Home version was in the Professional version.
Vista ain't so simple. Teachers and students really like to do digital storytelling, make movies and claymation. Windows Movie Maker and the new (and overdue) Windows DVD Maker is perfect and both are available in Vista Home Premium. The IT department also needs some advanced profile and group policy support. Both are available in Vista Business. However, Vista Business lacks Window Movie Maker and Windows DVD Maker. The solution, pay up for Windows Vista Ultimate or find third party solutions for movie making and dvd authoring.
Here are the Vista comparison charts I used.