The workstation is within 30 feet of the AP and when logged in as the Administrator it works fine, but when a user logs in he/she quite often gets disconnected and therefore loses his/her desktop and mapped drives -- a very inconvenient situation. Any ideas about where to start looking to solve this problem would be greatly appreciated.
I would like to more widely make use of wireless, but until I can solve this problem wireless deployment is out of the question. Thanks in advance for any suggestions.
I'd first try using Ethernet to connect the workstation to the wired network at the same point -- for example, just plug the cable currently connected to your AP into an Ethernet NIC or USB adapter on your roll-around workstation. See whether the same behavior occurs over Ethernet. If so, then you have a Windows Networking logon and permissions problem, not a wireless problem, and you can use typical NetBIOS troubleshooting tools like the NET USE command to figure out what's wrong.
If things are just fine over Ethernet, then you've isolated the problem to your wireless USB adapter. You don't mention whether you're using 802.1X authentication with WEP, but that could definitely be involved, because the new user would probably be re-authenticating with different credentials (e.g., user certificate, Windows login/password). If that's not it, look at the group permissions associated with the adapter's config files, drivers, etc. You could also try logging in with another user account that's not Administrator, but in the same Group. I'd use the workstation's event log and audit files to get further information about what's happening.