Hey Andrew...

I agree with Lonk that the script you supplied doesnt do any registry editing. It simply reads...And I dont think a PC would be usable if the users couldnt atleast Read from the registry. So either there is some other part of the script you did not post..Or its a bug in MS.

Anyways...There is a vbs script on WinXP Pro machines in the system32 driectory called prnmngr.vbs which will get the default printer for you. I didnt see if you have anything in the AD that isnt XP or not...But for the XP machines you can try...

Code:
If @ProductType = "Windows XP Professional"
   $tempdeffile = "%temp%\defprinter.xxx"
   $tempdefhandle = FreeFileHandle()
   If Exist ($tempdeffile)
      Del $tempdeffile
   Endif
   Shell '%comspec% /c cscript %windir%\system32\prnmngr.vbs -g > '+$tempdeffile
   If Open ($tempdefhandle,$tempdeffile) = 0
      While @Error = 0 and $defaultprinter = ""
         $line = ReadLine ($tempdefhandle)
         If InStr ($line, "The default printer is")
            $defaultprinter = Split ($line,"The default printer is ")[1]
         Endif
      Loop
      $null = Close ($tempdefhandle)
   Endif
   ? "Default Printer --> "+$defaultprinter
   ?
   ? "Press Any Key To Exit"
   get $
Endif