Try this mate

code:
 
If @inwin= "1"
$os_service = ReadValue("$Compname\HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion","CSDVersion")
  If $os_service = "Service Pack 3" OR If $os_service = "Service Pack 2" OR If $os_service = "Service Pack 1"
	 Run "G:\W2KSRVPK4\W2KSP4_EN.EXE -u -q -z"
  EndIf
EndIf
let us know if it works

Aaron
_________________________
If at first you don't succeed, try again. Then quit. There's no use being a damn fool about it. - W.C Fields