OK my thinking is a simple script which you put in the startup...
I have not checked this out and you may also need to read
this but so long as your remote users are in a situation where they are truly booting Xp I think this is very doable - after all utilities like partition magic do it all the time.
Sorry if this seems glib, but after you answered my question I fekt a duty to reply to back up my feeling although it is the wee small hours here and I am on my laptop so no time to back up my assertion with actual proof...
Let us know how it goes - I am sure a script may be forthcoming if you still have trouble