Several things that I would do.
1. Yes replace the hubs, with switches, getting rid of the 3coms and going with cisco catalysts.
2. Segment the buidling, instead of having every dataport feed into the srvr room, put a switch on the far side of the building, away from the server room, and then feed it to the server room. You save on cabling costs.
3. Label every dataport so that it corresonds to the port on the switch. use a ptouch label maker, it goes a long way.
4. Move to a single OS architecture. But not NT4 or SCO unix. If your going to stick with windows, move to 2K. If your going with linux, move to BSD or Debian.
5. If your sticking with windows, make sure you have 2 domain controllers. If the mail is public e-mail, then it should not have any other applications running on it.
6. Centralize your backups from 1 machine.
7. TES003 is a catastrophe waiting to happen. Any machine that holds mission critical data must be in a raid5 config with a hot spare. No exceptions.
8. If you want to get fancy you can have all servers installed with gigabit nic's, get a gigabit switch, so that segment can feed data quicker to the lower switches.
9. Upgrade your NAS, 40 gigs is nothing these days.
10. I don't see a firewall anywhere and what is the tes008 irm server linux'mailman' doing on the floor, and what is it's role.
11. When replacing hardware, I would go with a smaller footprint of server class. You have racks, use them: rack mount your servers.
there are alot of other things I would do, but this list would get you pointed in the right direction.
Plus, if you really want to get fancy, got to cdw's site and get some pricing on devices.
