Now, think of exactly what you have to do.

You have to DOS the network, and send all logged on users an error message stating that they have been disconnected, or no longer have access.

You could do one hell of a UDP flood, or any other way you intend, then do something as simple as broadcasting a msgbox to all of the logged on users. When this msgbox is broadcasted, make your final nail in the coffin cut off the WAN. There is alot of source code out there for worms that you can use. The MSBLASTER has a few techniques you could use, in the IP generation, and in the actual transmission of the packets. I can give source for MSBLASTER, or you can google it. I will not post it here, I will zip it and email it if you are interested.

Then again, I do not know the specifics of the assigment. Unless your looking to impress your instructor, why make things over-complicated?