WOW, thats a huge questions. Way, way too many answers lol. But the short of it is, there is no overall security that you employ, you
have to concentrate on each aspect of your network. The workstation OS's, make sure they are patched and read up on the security issues
for those specific OS's. Look at a firewall solution for your head end to the internet. And there are security issues on software too. Email,
dhcp, dns, ect, ect. Your hubs/switches/routers on the network, read up on your manufacture recomendations for those pieces of hardware.
Make sure you have good passwords on EVERYTHING. (workstations, servers, printers, hubs, routers, switches, etc etc)
min of 8 characters with a mix of upper and lower cases. There are whole libraries on security issues and forums (Anti Online, etc), and and
and and lol. Better start reading d00d!