Well back to the original topic, yesterday I upgraded a friends laptop from Xp to Win7 x64 Home Premium and I installed VPC 2007 SP1 x64 and created a WinXP VM in it from their laptop XP disc and all went well. The only thing I noticed was VPC had a warning that Home Premium isn't an officially supported OS but it all runs fine.

As for Vista/Win7, I'm running Win7 Ultimate on both my computers and my Vista VM is a 32Bit Ultimate edition there so I really don't know what's missing from the other editions.