I believe Xpmode is more than just loading virtual pc and then a licensed copy of xp. This will work (and does not require hardware Virtualization) because I've done it in the past. It has it's limitations however. Xpmode is much more robust and requires hardware virtualization (VT). So there is a difference.
There really isn't much that is "more" robust about XP Mode. The only real advantage to XP Mode is the licensed copy of Windows XP and the fact that you can access the applications loaded within that virtual machine directly from the host itself.
With that said, I've found the performance of XP Mode to be awful compared to either VMWare or Sun VirtualBox. I'm not sure what Microsoft did to accomplish such dismal performance, but I've discussed it numerous times on the technet forums and other than using another product, there really isn't a solution.