Connecting PC's to our mac network

We have a 10.4 server that puts out our internet to all ethernet hookups. We also have 2 wireless airport extremes. Our mac computers can connect VERY easily, just by plugging in to the ethernet ports, or wirelessly by entering the password.

PC's however, are very different and difficult. Each time a PC wants to connect to our network, either via wired or wireless, I have to manually go in to the network settings on each computer and set up an IP address, gateway, and all that stuff. It gets very old because I am a teacher and most of the time I need to do this is when I am in the middle of class.

I was not the person who set up the network or anything on the server, but i DESPERATELY want to get it to where they can just plug in and be connected or enter the wireless password and be connected. Currently, when the PC's try to connect to the airports, it will let them connect they just don't actually have an internet connection (i.e.- when they go to a website it says not connected to internet).

Any help on this would be GREATLY appreciated!!