it is nice and easy... if you get a router with a modem built in.. make sure it has a firewall enabled... otherwise if 1 computer connects to tinternet, and the otehr computers connect thought it.. make sure that computer has a firewall on it.
Firewalls are not optional unless you want an early grave.
also, make sure that peopel know how to unshare directories that they dont want other people to have access to.
finally.. what is your plan for data backup..
if you are using winxp pro these is microsoft backup built in.. use this to backup the data on each computer on 2 other computers.. just in case.. and then burn to cd
good luck