as this is an old thread resurrected, you should make clear who you are addressing, people who posted in this thread originally may not still be active in the forum

i have tested wmi in both vista and windows7 (home premium) as a limited user, works in both, but the return strings have to be decoded
in vista the return is in ascii
but in widows 7 the return is a hex string
in either case it easy to process the return to get the correct value
should be able to figure from the length of the return whether it is ascii or hex
as admin user the correct value was returned directly from the wmi query in vista, have not tried that yet in windows 7

i have also made an api version that asks for elevation, then it works correctly with admin password provided