Ok here is the deal;
I want to setup a home network so I can get on the net with more then one PC.
My ISP requires me to log in though a DHCP using PPPOE and needing a username ad pw every time I wish to connect.
I connect directly to an ethernet socket in the wall. I have no modem. The whole student flat I am in is one big LAN.

When I browse though tutorials describing how to setup my own server, I always come to a part mentioning running my own DHCP server.
The thing is that if I would run a DHCP server of my own, I could disrupt the hole building's ability to dial in.
My own DHCP server could be answering to login calls from anyone in the building before the ISP's server, making their login attempt fail.

I either need a way to route traffic from and to my other computers without a DHCP server, or make ABSOLUTELY SURE my own DHCP server would never respond to PPPOE dial in requests coming from the building's LAN.

I have no problem figuring this stuff out from tutorials, but I need to know beforehand how to exactly NEVER have my DHCP server configured.

edit:

I am only allowed to dial in to the flat's LAN once. One connection, one IP. I am not behind a NAT of any kind though. I have my own, real IP.

Thank you for reading and thank you in advance for trying to help.

You should have a router connected directly into that socket in the wall. You should have it configured to establish the pppoe connection on the WAN(Internet) network port. Then you would have your router set up to serve DHCP requests through your LAN(local) network port.

Your router could be a regular SOHO device or a PC with more than one network card. As long as you make sure you configure the DHCP server to serve request only on the local network everything will be fine.

Ok, let's say that you're plugging in a 4 port router. The router will have 4 LAN ports, which you will plug your computers into. The router will assign IP addresses to computers plugged into the LAN ports via DHCP, but not to the WAN interface. You will have to log into the router, set the WAN interface to use PPPoE, and enter the username and password. At that point, it will all work.

Note that PPPoE and DHCP are mutually exclusive; PPPoE assigns IP addresses without the use of DHCP; even if you were to plug one of the LAN ports to the wall jack, the upstream PPPoE server would simply try to authenticate against the router, which would be trying to serve an address via DHCP. The authentication would fail, and that would be that.

Are you assigned only one IP address per outlet? If not couldn't each host run be a client of the buildings DHCP server.

If you are given a single IP address, either use a NAT router or add a second interface. A router would be a DHCP client on the input and a DHCP server on the LAN switch. The NAT function would allow you to share the IP address with the hosts on the lan. Another option is to use your computer as a NAT

This is actually very simple to do. You need a router with a "WAN" port though. A WRT54GL (or WRT54G) is a good example.

Plug the WAN port of the WRT (or similar) router into the wall, and then you can run a DHCP server on the "Local" or "LAN" side of the router. The router has this as an in built function. Below is a screen capture from my WRT54GL (I'm running custom firmware (DD-WRT) on it.)

http://img239.imageshack.us/img239/8138/78675522wm2.png