In the schools I have worked for and gone to Generally their network set up is very simple. It is a LAN (local area network). They will have one line comming in from a major ISP in the area (the band width will depend on the school size). From there, most will have it set up so it requires some sort of authentication before getting on to the network (although many dont). and they will have various servers around campus hosting a variety of things, most universities have masive file servers for student and staff use, they may host their webpage, as well as run servers doing various other tasks (email, firewall, proxie, media servers, etc. etc. etc.)

As far as blocking the P2P software they do it several ways. 1st, they will generally block the common P2P ports. This is done for two reasons. 1. to stop the majority of average users from using the service 2. it helps deminsih the arguemnent that you didnt know it was against the rules. From there, many larger schools have monitoring software set up and if any single IP address is taking up X amoutn of bandwidth for X amount of time, it is cut off and the MAC address/Username and Password are now banned until you contact the admins. It is watched especially well if your computer is uploading large amounts of data, not just downloading. Their reasoning may be something along the lines of "it was suspicious activity and also a symptom of possible virus infection. From here, there are suually policies that state you must have one of the helpdesk people/it staff "clean" your computer before unblocking anything. This gives them the chance to look for P2P software and take note of it.

Of course it can be argued that you were downloading legit stuff blah blah blah and they have to unblock you or they can get in trouble.

Warning: Do not use P2P progrmas if your policy states they are not allowed. It is grounds for Fines/suspension/expulsion if you are found out. Although it is a harsh punishment, generally for problems like this schools like to make examples out of people. The reason? becasue your ISP will see the traffic, and generally the school will see a notice saying "this IP address is uploading/downloading pirated stuff. make it stop or we will" (I have seen many of these emails, so we hunt the person down, cut them off or we get cut off.