If you have attached all computers to a switch you can setup a samba server on a linux machine other than the router.
And you won't need a firewall on that machine because all external traffic goes throug the router.
Because you use a switch all is automatic and you don't need to setup anything.
You don't need to use a DHCP or DNS server on that machine.
If you use hostfiles on all machines that isn't needed.
Because the local network doesn't go through the router.

You can edit the hosts file on the windows computers.
It's on C:\WINNT\system32\drivers\etc\hosts (on w2000 machines).
But you have to edit it with an editor like EditPad lite (NOT wordpad).

But you could also use a DNS or DHCP server on a linux machine other than the router that's up to you.
Using fixed IP-addresses makes it simpler, and you see what you do.