Difference between Pro and Home versions

Does anybody know the real, low-level, differences between the 'Home Premium' and 'Pro' versions? I know the obvious stuff but the absolute showstopper for me between the XP versions was the complete lack of 'User' and 'Group' management, and no ability to apply file & share permissions using them in the Home version - Is W7 the same?
I gave up with Vista after 3 weeks of trying to use the RC1 version and eventually deleting it before I threw something big and heavy at my monitor, but they seem to have taken away most of the really annoying things in W7 so I'm prepared to go with it. Unfortunately the Pro version is twice the price of Home Premium so I need to know if I really have to shell out so much for it?
I've scoured the MS site but it's all brochureware and no real information - anyone know (Maybe it will be the same as for Vista - does that have user & Group management in the Home versions?)

 

The defining difference for me was learning that my Acronis True Image and Disk Director work just fine in Windows 7. Now I can buy the Home edition which does not have the MS imaging/backup facility.

Roger