Need internet connection monitoring software or proxy server

[Chop]

Hi there,

I need software that would force users on the network to login to access the internet, this software must then log the amount downloaded etc. and a nice to have would be to allow me to disable certain ports (i.e. iMesh, e-Donkey).

I have an adsl modem/router with an usb connection and use Windows XP, I'm thinking of installing Linux on the server. This is for a very small office but bandwith is limited.