You haven't installed XP to the Virtual PC yet.
11. With the Virtual Machine shutdown (not suspended) ZIP the files (I put my VPC's in their folders, as well), so you have a 'virgin' copy should you need to setup a new VPC, revert, or whatever.
PS: Yes, I know you can create differencing disks, but I find this easier. Plus you can still use these Virtual Disks in a differencing setup, if you like, by running the disk wizard, afterwards.
PPS: I have multiple 'virgins'. eg with XP, going from the original retail, through SP1 and SP2, with variying IE versions, etc. Yes it's become bewildering, and yes, the earlier ones rarely get used any more. But they're there, should a need arise - that reminds me, I should check that they haven't become corrupt... :O
PPPS: Those Microsoft IE VPC images use a demo OS don't they ? as in will expire ?
EDIT: Just read the download page: "This VPC image will expire on April 1, 2008.".