I have never tried it yet, but some ideas:

1. In NT-Reskit, isn't there a script to run a program as another user? Maybe this might be enough for you.

2. It might be possible to write a program (e.g. with Tk), that stays on top all the time (binding all possible events to a method that puts it in front of all other windows, e.g. $toplevel->deiconify(); $toplevel->raise() If you remove the decoration (e.g. with $toplevel->overrideredirect(1); ), it couldn't be closed any more with the mouse. There's just the problem with alt+f4...

Best regards,
perl -e "print a|r,p|d=>b|p=>chr 3**2 .7=>t and t"