I'm no expert, but this worked for me. I got an Alcatel speed touch home. It has an ethernet interface. There are websites that tell you how to hack it to become a speed touch Pro. With the speed touch pro you can set up NAT. Then you get yourself a cheap 4 port ethernet switch.
There are a lot of people who can explain it better than I can, but it works like a charm. Your moden stays online 24/7 and reconnects itself if need be. The modem also acts as a kind of firewall in this case. I have two computers and it's like internet is a permanent part of the LAN. It's very cool. Anyway, I don't know if the speed touch home is easy to find or not. I got mine here in France. It's only slightly more expensive than their crappy USB modem.