Ed Bott does a nice job of furthering the XP Mode/Windows Virtual PC discussion with a look at which processors actually support this new Windows 7 feature. And that's important, because if your processor doesn't support it, you can't use it.
A heavily hyped new Windows 7 feature, XP Mode, won’t work on some Intel-based products? The problem is caused by the Byzantine way Intel packages its CPU technology—adding, removing, and tweaking features like bus speed and cache size to hit the widest variety of price points for PC makers.
The new Windows Virtual PC (now available as a beta release for the Windows 7 Release Candidate) requires hardware-assisted virtualization. For your PC to run XP Mode in Windows 7, the CPU has to support Intel Virtualization Technology (Intel VT) or AMD Virtualization (AMD-V), and this support has to be enabled in the BIOS.
In the case of Intel’s phenomenally confusing product matrix, VT support is added and removed from CPU models for reasons that have more to do with marketing than technology. You can’t necessarily tell from the model number whether VT support is present or not.
Tables ensue. Useful tables. :) Please refer to the original post for more information.