I was just suspended from school. Apparently, my IP address was used to drop another student from his class. I told them I was somewhere else and provided proof (receipt) but they still believe that I was involved.
Your IP address? Do you live in university housing, or off-campus? Do you have a wireless access point that might not be secured? What kind of proof have they given to you at this stage, if any?
Your "IP address" shouldn't give anybody access to drop a student from a class. That type of operation requires some form of authentication (username/password, or token, or some unique identifier). These credentials will be far more telling of who actually committed the act in question.
Depending on how they assign IP addresses, it can be VERY easy to arbitrarily use somebody else's IP address. If they assign then automatically (via DHCP), then there should be logs of what MAC address (a unique identifier to each physical network card) was given that address at what particular time.
However, there is another layer to it. IP and MAC addresses are easily changed, especially by somebody with some level of technical skill. IP addresses do not hold up in court as a form of authentication (proving somebody is who they claim to be), unless the address is assigned by an entity to somebody/something that cannot be altered by the receiver. An example of when they CAN hold up, to clarify what I mean, is when an IP address is assigned to a user on a dial-up modem. This is because the IP address is assigned to a physical phone number that the phone company can correlate to an address. Proving that the person using the computer on the other end of that phone line, however, can be difficult.
The long and short of it is, the charge is bogus. Your school cannot prove that you were the person using that IP address at that time. They may claim you were associated with it, but unless their IP assignment is iron-clad (and I highly doubt that) then you can just as easily prove it could have been anybody smart enough to change an IP address to attempt to avoid detection.
As others have said, don't sign anything at all. You need to speak with an outside attorney to discuss your options and how to proceed.