Looking at the @PRODUCTTYPE I stumbled accross the function, so would this work since I only what the command to run on XP/Vista domain PC's and not when they login to a remote server session

Function IsNonServer()
if not (IsMemberServer() or IsDomainController())
$rc = WriteValue("HKEY_CURRENT_USER\Software.......)
else
$IsNonServer = 0
endif
Endfunction