If you are like me and wanted a comparison on which edition of Windows Vista to buy, you could just visit the following Microsoft.com site http://www.microsoft.com/windows/windows-vista/compare-editions/default.aspx to get the best idea of the features you would like to have and decide accordingly.
Most of the editions today come with SP1. So, many of the compatibility issues with a lot of third party solutions have been fixed now.
The Windows Vista Ultimate, needless to say, is the best you could think of and if you are targetting Media Center, Collaboration etc., this is the one you should be going for.
Thought of posting this link since it took sometime for me to figure out even from the windows vista official website, this particular reference.
Cheers !!!