To add to my previous post about the guidance around Windows XP Mode for small/mid size businesses. An update was released to allow Windows XP Mode to be deployed to systems without hardware virtualization.
The update to Windows Virtual PC to support running on systems without hardware virtualization is now available for download. You can grab it here:
You can also read the full KB article here: http://support.microsoft.com/kb/977206
Ben has put some more great details on this up on his blog.