Because Stevae, he is not going backwards, he is installing the freely available version of XP virtual machine for apps that don't run under Vista/7. Windows Virtual PC with XP Mode is free to 7 Pro, Enterprise and Ultimate users.
Do some research on it, it is actually a nice feature for anyone upgrading from XP/Vista to 7.**********************************I would go with the 64bit unless you have apps that just won't run under 64bit at all.
But I think you might have that problem on 7 64bit also anyway. It would be time to find something 64bit friendly. If you don't need 32bit, there is no reason to stick with 32bit.
32bit should be dead by now, and damn the consequences.
I think the main purpose for the VPC with XP Mode is for...