I run Win7 on my laptop (and I really, really like it). I'm not sure, however, of whether you can run XP in a sterile environment using XPMode. My first inclination would be no - the XP mode would be strictly for backwards compatibility, and other programs installed on the machine would impact this.
If, however, you install Win7, you could then use your old WinXP license in VirtualPC (assuming you purchase a Full version of Win7, and not an upgrade). That would certainly satisfy the requirement, and would give you a Win7 machine with both a XPMode and a VirtualPC with a WinXP guest OS. You could then install only Access 07 Runtime in THAT environment, which would be a "sterile" environment.