Networking question

Could I set my network up like this?:
  Modem -- Switch -- Computers
My current setup is like this:
  Modem -- [Computer, Router -- Computers]

What I really wonder is if DHCP will work with several computers on the same port on the modem (which has four ports).  If I had a switch I could try this of course, but the case is that I do not have one (and I do not think I could configure my router into being a switch).

>>7
Well, your router gets its IP from your ISP's DHCP (unless you have a static IP).  The normal configuration is for your router to boot up and then check the network for an IP. 

In a similar fashion, your computer gets its IP from the router's DHCP.

If your modem has the ports I described (1 WAN + 4 LAN), then yes, it's a router and is probably routing as we speak.

however, if your ISP gives you four static IPs, you don't need a router at all.  your basic setup is: internet -> (firewall would go here) -> switch -> computers.

you will need to disable the routing function in your modem/router/switch, if you can.  you will then need to manually assign each ip to each one of your computers, and then connect each to the switch.  using this setup each computer needs its own firewall.

notice in the above diagram that the firewall needs to go between the internet and the switch.  if you can disable the routing function in your modem, you can use your bsd machine to act as a firewall.  you will then need another switch after the firewall, i.e.

 internet wire -> modem/router with routing disabled -> firewall computer -> switch -> other computers

what model of modem do you have?