Register a domain name and point it to your IP. It's not really hidden since users who know how can just do a DNS lookup on your host name and get it. At least visitors to you website won't have to type in your IP address though. There's no way to hide your IP completely if you are going to host a website because IPs are the basis for the internet, and without them, nothing would work.
You can either manually update the DNS entries on their web site whenever your IP changes, or you can try one of the linux perl-based scripts.
For $75, you can buy your own domain at places like nic.com. And then just use hn.org for the dns host, and you can serve www.whatever.whatever off your computer.
Oh, and incase you didn't know, you can enable web sharing in the system preferences, under 'Sharing'.
It's not that much to register a domain name. More like less than half that. I can register a domain name with www.easyhosting.com and have it parked for $19.95 Canadian! And if you don't want to go with their hosting package, you can easily change the DNS entry to whatever IP you want.