Cheok,
We admire your persistence and we thank you for interesting feedback and insightful questions.
Do you have any error or warning entries in the Windows Even Log (Application)? For us, in order to make UltiDev Cassini for ASP.NET 2.0 work under NETWORK SERVICE account, we had to grant NETWORK SERVICE "write" access rights to "C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files". Until then we had all sorts of problems. Once we made the change, we were able to access Cassini applications from other computers on the network.
If you have were able to access your application from another machine in the Intranet scenario, then problems with Internet are almost certainly related to the network setup, like firewall settings, port NATting, software firewal rules, etc. From the web server perspective, when connection is accepted - server has no way of knowing where it has originated - inside the LAN or on Internet.
One thing to keep in mind, that Windows XP may have as few as two inbound TCP connections allowed. Although this should not be a problem for Cassini, which does not hold on to open connections due to the lack of "keep-alive" support, if there are any other server apps on your hosting machine taking up inbound connections, you may see TCP connections timing out, which usually takes two minutes.
Best regards,
UltiDev Team.
Please donate at
http://www.ultidev.com/products/Donate.aspx to help us improve our products.