Which Ports Need to be Open?

I have a W2k Server Machine running Proxy 2.0, also have another W2k machine that is hosting a website. I have a list of all the different ports – what I would like is a list of the ports that need to be open on each of these machines. The proxy server is dual honed with a nic for the internal and ext. network. Currently all ports are open on the ext. nic on both machine and I know this is a security problem. Thanks Jeff