Want to setup an intranet for a small business setup.
Current Setup
28 computers running Windows ( few older pc's run Windows Xp but most run Windows 7)
Spare Dell Pentium 3 which can run as a server.
6 switches spare NIC's and lots of lan cable available for networking.
3 Independent Internet connections
Currently we have 3 independent networks which share internet connections, each network uses a different internet connection. Current network is setup solely to share the internet connection.
What I need to achieve in this intranet
Setup one common network.
Instant file transfer via local network (maybe setup a file server?)
Local text and voice messenger software
Bridge the 3 internet connections and route all the internet connections from the main server
Ability to allow or deny internet access to any computer on the network.
Remote access from the main server to the client pc's on the network to debug software issues
What operating system should I use on the main server? Do I need a hardware firewall?
Any setup guides / resources or how-to's on how I can achieve the above requirements.