Here is how we do it at work...
Outlook (NOT OUTLOOK EXPRESS mind you) uses .pst files for everything. We have ~50 users, and we have everyone's .pst files residing on the server. Here is how you do it. Open outlook, right click on Personal Folders (in the hierarchy, it holds inbox, outbox, sent items, etc.) and click properties. In the first tab, there should be a button entitled "advanced". Hit it and find where on the hard drive the .pst file is stored. Relocate that file to the server. Next time you open up Outlook, it'll ask where the .pst file is stored. Navigate to your server where you stored the .pst file, and from now on it will default to that .pst on the server.
On machine #2, find where outlook is storing that .pst file, and simply delete it. Then when Outlook opens next, it'll ask where the .pst file is. Navigate to that same folder. Now both are using that same .pst file.
I'm sure there will be some kinks found here and there, but your obviously rather suave when it comes to the computer anyway, so I'm sure you can figure it out. If you have any questions, we may can help, but remember, this forum is primarily for use as a Computer Graphics specializing in Architectural Design forum. This problem doesn't exactly pertain to this forum. But, we seem to be pretty nice people, so we can accomodate once in a while.
Hope that helps!