I registered here at amiga.org just to reply to this post. You say that using a NULL modem connection to an NT system was the only solution to get broadband internet for your A500? I beg to differ! Why not just use a serial-to-CAT5 similar to this one
http://www.ipcas.de/english/products/ipether232telnet/ipether232telnet.html You can use this built-in virtual modem to speak to the device and simply plug the adaptor into a router, hub or directly into a cable/DSL modem ... cool, eh?

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I went the NT Server route for 2 reasons.
1. Yes a modem would have been easier, but I wished to share my ISP cable/broadband connection from the Windows machine. I already had NT 4 Server, so no extra cost. No NIC card for my old A500, so Null Modem was the only solution.