Outlook Causing High Processor Usage

I have one client on my network that is having problems with Outlook.

There is a several second delay with every message he opens, replys to or
forwards. When I look in the task manager, Outlook is taking 100% of the
processor time during this delay. After the delay the message opens and
everything is fine.

This is only occuring on this one client, all other clients are fine. The
machine is Win2K SP4 with Outlook 2K. We are in an Exchange environment and
do NOT use PSTs.

I opened his mailbox from a server and all the messages opened right away.
I defraged the client machine, no difference. I repaired and reinstalled
Outlook, no difference. All other network activity and browsing (local and
Internet) is fine with no delays or excessive processor usage.

The user says this just started one day. For years it had been fine.

Does anyone have any ideas what could be causing this?
Thanks.

Peter