Thanks to Noam Rathaus for the tip: Microsoft has posted a new "getadmin" hot-fix for Windows NT 4.0 Service Pack 3. This hot-fix addresses a new version of the getadmin hack, which was recently released. Getadmin grants normal users administrative rights by adding them to the Administrators group. This utility can be run from any user context except Guest and grants a local user account administrative rights. It does not affect NT 3.51.
You can download the new getadmin files on the Microsoft FTP site