Hi I don't even have Windows XP, but how do you know ParPort.sys isn't loading or that it needs to be? Is there an exclamation by that device in Device Manager and when you read more about it that's what it says? It just seems to me that Windows XP might not use that file anymore. Also why don't remove it again and then let windows auto-detect it. If it isn't autodetecting your Pritner Port make sure it's set to Auto in your BIOS. Also make sure you have PNP enabled in your BIOS (I doubt XP will let you install without this option enabled, but who knows). Can you be more specific as to what your problem is. IE I go here and this is bad..... Also I've had power supplys go bad on me and my serial ports would stop functioning properly. It's possible that your Parrallel port could stop functioning for the same reason. Also what kind of Motherboard Chipset do you have? What parrallel mode are you trying to use? SPP, EPP, ECP, BIDR? etc..
Good Luck,
Christian

I know paraport.sys isn't loaded because it doesn't appear in the loaded modules list in msinfo32.
 
I deleted it from the 'non-plug n play drivers' list in device manager.
 
However I have found it's key in the registry, does anyone know what value will reload it to 'on demand mode'?

Why don't you just undo what you did: Add the driver back to device manager. Rather than trying to decipher the registry.
-Christian