We have a very difficult/weird problem. When users type emails Outlook simply hangs. At first I thought it was a specific user/client machine and I formated it. . .but then another and another. Then I thought the problem is on the exchange server. So I defragmented the store and the server. I rebuilt the profiles . .
But your issue is with creating the message.
If you can, load taskmgr/procexp to see what happens when you start typing.
Procexp has more info. Maybe a service is doing something.
Assuming it is a file access thing, use filemon to see what app/files are being accessed.
Make sure you unload all apps and stop all unnecessary services (on the workstation) whilst testing this out.