Windows 7 Drops XP Hardware Virtualization Requirement
Windows XP mode running simultaneously with Win 7. Image by Paul Thurrott
Both AMD and Intel support hardware virtualization (AMD-V and VT-x respectively), but AMD restricted the technology much less than Intel did. Intel opted to use VT-x as a premium feature, which led to spotty coverage and occasional customer confusion. At one point, Intel had a line of 45nm quad-core processors that were running cheaper (and faster) than the older 65nm Core 2 Quad 6600. The difference between the two was VT-x, the Q6600 supported it, the other chips didn't.
Happily, this is no longer an issue. Microsoft has removed the hardware virtualization requirement for Windows XP, making it available to businesses and consumers who may have previously been unable to utilize it. The updated version is available here; there's no word yet on any performance differences between hardware and software virtualization.