Jedis,
Need some hardware info on your boxes but this is how I would do it (with windows and static ip address):
1. Install win2k server on 2 of the boxes. Make sure you install as well DNS, Wins, DHCP and AD. Then install exchange 2k on one of them. If you have your own domain then you will have to set up an MX record in the "external" DNS to point to the ip of your box that has the mailserver on it.
2. Actually, on second thought, I would use terminal services in win2k - Install win2k and then install terminal services via the add/remove programs applet. You may have to install a terminal server license server on the same box as well but that should not be a problem as xp has built in licenses for access

Then on the client systems you use the "remote desktop connection" (in accessories/communications from the start menu) to connect to the ip address of the termserver; your destop and settings will be the same from wherever you log on from, it is like running a virtual session from the server. Whenever you want to install apps onto the terminal server make sure you drop to a command line and type this:
change user /install then when you are finished installing type:
change user /execute
This may serve you better (the terminal server) without the need to set up a domain and all the overhead that goes with it and you can set up outlook express or whatever mail client you want to access any email protocol just as easy and you can be assured that from whatever pc you log on from you will have the same desktop
You may have to set up user accounts for each user on the termserver though, I have always used TS in an NT domain environment that does all the user authentication, just make sure you are all on the same workgroup
Hope this helps some
/JD