ugh! I believe that companies like Olarm (
www.olarm.co.za) developed a device that connects to that serial port to "turn your alarm into a smart alarm". A good friend of mine has just installed Control4 into his home and I popped around while the installer was there and I asked about alarm support for which they support Paradox. Control4 also have a device that connects to that serial port.
Ideally it would be great if there was a hardware bridge that would connect to this serial port and allow you to connect an Ethernet cable to it. At the moment, I'm pinning my hopes on the IP150 (with a firmware downgrade or an old IP150 with old firmware) as I doubt such a device exists.