If it appears that Win XP is not shutting down, give it some time. Some users have reported a minute or longer for shutdown to visibly start. Thus far, it appears that this is a consequence of software that is running when shutdown is attempted, and it also may have something to do with particular hardware. If you are experiencing this problem, be sure to close all running programs before attempting shutdown and see if this solves your problem. If so, then you can determine, by trial and error, which program(s) are involved.
One specific solution for this was provided by Microsoft support. ” In Control Panel | Administrative Tools | Services. (You can also get this by launching SERVICES.MSC from a Run box. This utility is also built into the Computer Management console.) Stop the Nvidia Driver Helper service. Many other friends quickly confirmed that this solved this “extremely slow shutdown” problem for them.