I understand the pain of losing data, I'm a hardened techie but lost data always has my empathy.
There's one easy way to know if you have a valid virtual disk, simply, the size of the .pvm package, in Finder, navigate to the folder that has your virtual machines (~/Documents/Parallels by default), select the <virtual machine name>.pvm, right click on it and select "Get Info" from the context menu, look for the size, if you have a valid virtual disk with Windows it should take some GBs (at least 5 GB I would say). If it's just some MBs, then it's impossible to have a valid Windows XP installation in there, the file is corrupted, useless.
You can also check the size of your .pvm in Time Machine backups via the same method in Time Machine.
Last edited: Jan 27, 2013