I'm going to go out on a limb and say you don't have to worry about drive Z on an NT machine.

I base this on the following Microsoft Tech paper.

This paper talks about why 95/98 needs to use drive Z to connect to the NETLOGON share, and implies NT knows where NETLOGON is, and does not need to use a drive letter.
http://support.microsoft.com/support/kb/articles/Q136/0/73.asp

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