Windows XP Mode is a pre-configured solution for Windows 7 users needing support for older software, and, until recently, it required AMD-V or VT processor hardware. An update released today should make XP Mode far more accessible to more Windows 7 users.
If you're a 7 user who's been trapped by the lack of that finicky hardware requirement, check out the XP Mode page later today and look for the update. Those with Intel or AMD processors sporting virtualisation code will still see benefits, but now you can run XP inside 7 solely on the back of your processor and memory, if that's what you need to do to ensure legacy program compatibility.
When XP Mode gets its update, check out the How-To Geek's XP Mode installation guide. You can also still use XP Mode outside of Microsoft's own virtualisation window by running it as a VMWare image, and run it on any version of Windows, regardless of licence or hardware.