Windows XP Shutdown Time

I am having a problem shutting down my system with Windows XP Pro. After all of the users are logged off and I am at the welcome screen, it takes the computer anywhere from 3-5 minutes to restart or shutdown. I have tried running disk cleanup, defragmenter, and scandisk, but I continue to have this problem. I have also made my paging file size to the max possible. However, I do not have any problems when booting - it takes about 20 secs to boot.

I have a P4 2.4 with 512 rdram and a 120 gig hd.

Does anyone know what I can do to increase my shutdown and restart time?

Thank you.