1) That is a Windows question, not a Parallels question. You would be best off researching at MS or elsewhere on the internet for Windows help
2) I frequently copy my XP VM folder to an external drive for backup purposes. Actually whenever I make a significant change in the VM. If your normal VM gets corrupted or infected, just trash it and restore from the external drive. It is the equvalent of a clean install of Windows on a real PC. The XP VM folder is found in ~/Library/Parallels/
If you run a VM created on one Mac, on another, I think XP may recognize the hardware change and demand an activation. (Similar to installing the XP on 2 PCs using the same serial number). If the "different, valid number" you are referring to is another XP serial number, I have no idea how you would enter it in the copied VM. Not sure if the XP serial number can be entered other than during an install.
Last edited: Mar 18, 2007