I've never heard of a provider specifically precluding port forwarding before. When I was at school, we were directly on the internet and were not permitted to set up a router, to connect more than one machine but that's as close as I've experienced. If you have your own router that you administrate, you should be able to set up port forwarding and the provider would have no knowledge about it (nor would they need to since it's a standard operation that happens behind the scenes).
Assuming you are using your own router, you would just log into it, go to the port forwarding settings, and add an entry for external (internet/WAN side) port 80 to go to your HG machine port 80 (intranet/LAN side). This is not anything that would violate a typical EULA since it's a typical thing for a reasonable person to do. UNLESS of course your ISP has some reason to ban hosting web sites. If that's the case, then you would technically be violating that restriction. It's a personal site for your use only, but it is a web site none the less.
Either way, I can't see this as a problem for the ISP but if they have a rule against it, then that's how it is.
