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What is the best "port watcher" program
If you are looking for an actual port watcher (also known as a sniffer) try WireShark (previously EtheReal). If you are looking for a software firewall I would tell you to pack your bags and head home because they take up a lot of resources you could save yourself by buying a hardware firewall.
This can be as previously stated a Linksys, D-Link, Netgear, Cisco or even Trendnet. But you could also take an old machine (80486 laying around anyone?) and install IPCop or another Firewall OS and create your own system that is 100% customizable.
But again this is all just my ideas. You do as you see fit.