These questions here and here address the same issue but for Windows 7.
Unfortunately, we're stuck on Windows 2003.
Yes, we want to migrate but we have a custom, arcane piece of software tied to Windows 2003 and lack other options at this juncture. Please no suggestions about moving; we know it's a problem and are exploring alternatives.
On Windows 2003, how can you exclude all network traffic, except web traffic, i.e., packets via ports 80 & 443?. There doesn't appear to be a way to configure firewall rules.