In my office in school I just built today with Chris (our undergrad guy) the most complicated network I have ever build. Here is how it works:
First, there are only two ethernet ports in the room (the advisor pays much for each port, and we are not allowed to have routers) and 6 PCs and 1 Mac. Erdem's computer is directly connected to the first ethernet port. So we have one ethernet port for 6 computers, a 10Mbit router and a Gigabit switch and lots of gigabit ethernet cards.
From the port, the feed goes directly to my ethernet card. My computer is the only one that appears outside. Now, I have a second ethernet card installed, which is connected then to the 10Mbit router. I share the internet connection through my computer from out card to the other, so the router now has internet.
In the router we have connected the Macintosh and one more of the PCs (Chris needs the 4 remaining PCs for setting up a parallel network). This specific PC needs to have internet but not the rest 3 of them. However these 4 PCs must be on the Gigabit switch for the cluster. So, each one has a network card and it is connected to the switch. The one PC with the 10Mbit internet from the router has a second network card just to connect to the switch, apart from the one for the internet. Phew!
