My guess without testing it is that WMI on NT4 does not support the information you're trying to return.

Just because you have WMI installed does not mean the OS supports the call. There are WMI calls that are specific to every OS. i.e. There are many calls in 2003 that NT/2000/XP do not understand, there are calls for XP that NT/2000 do not understand.

I'm not saying that NT4 does not, but you would need to try and track down and run some of your own WMI test scripts, and/or read some WMI documentation to see if the call is supported on NT4 to know for sure.