Office apps hang, use 25% CPU

I have a handful of users running MS Office 2000 on Windows 2003 Terminal
Server who are having a problem. They'll be working in an application, with
other MS Office apps minimized in the background. They'll go to switch to
the minimized app, and it appears to be frozen. Bringing up Task Manager
shows the offending app is running at 25% of CPU. This happens most
frequently in MS Outlook, but it does happen from time-to-time in Word, Excel
& Access. Whatever is running doesn't time-out. It'll stay pegged at 25%
'til the cows come home.

There are four users who have this problem several times a day. The other
twenty or so users don't experience this -- ever. I've tried deleting users'
profiles, but it hasn't helped. I can't find anything unusual in these four
users' accounts that isn't in other accounts (e.g., group memberships,
security settings, application configuration). Has anyone else run into this?
Any ideas?