Kemp, I know you've covered every base imaginable, but would you mind looking this thread over- again -if you haven't already. There were a couple of users with XP who managed to get running, having the same application error you had at one point, with the info they reference in the Vista thread.
I know some of this you've tried before, but let's take another run at it, specifically the DEP AND the Runservice items. I know you've done the first, but I'm not sure about the second. In any event, take a look.
Cannot start OOTPX