Hi
If you want to connect to a large business network eg with a domain you need pro not home
If you need virtual XP for keeping old programs running and you do not want to learn about virtual pc's then again go for pro version
It includes both virtual PC and free XP licence
Beyond that are ultimate & enerprise versions with full disk encryption if you need it
For most people home premium is good enough
I bought pro upgrade because it was going cheap when win 7 was released
Note choice oem system builder or retail or retail upgrade versions
Best to get 7 with integrated service pack 1 to save time upgrading after installing
Regards
Mike Barnes