Choosing The Right Vista
VIA Arena has a very good guide to choosing the right Vista for your needs. There is a handy chart that shows you which features are in the different versions of Vista and what they mean to you. This is good reading for those of you planning to upgrade to Vista.
At a glance, here is a list of features that are not in every edition of Windows Vista. If the table cell is highlighted in blue then the corresponding features are in the corresponding edition of Vista. This should be your first place to look. If there are features you need or want you'd better get the edition that has them.
