The Contextless Login Extension for Window 9x and Windows NT allows for contextless login without requiring catalogs on the backend. This extension searches specified locations in the tree for all occurrences of the username. If one exists, LgnCLW32 automatically updates the context field of the NDS Tab.
If more than one exists, the user is presented a dialog where he may choose which context is to be used.
Please see this article for a workaround to a possible problem using this tool, as reported by Mark Saunders.