behind a router?
filter port 80 (http) on your router for web access and point it to your IP (internally 192.168.1.XXX)
start up your web server (if it's OSX client, then it's just controlled by the system panel, or if you like UNIX, bring on the command line in /etc/httpd
bring up your web brower and point it on to: http://www.dnsupdate.org/
download the app, then create your account at dyndns.org for your web site.
install the app, patch the kernel, giver a good old reboot for good luck.
load up the app and create your account in the app window. If you are behind a firewall or router (by the sounds of the other posts, sounds like you are) use the (behind firewall option) in the ethernet settings option
wait anywhere between 24-72 hours for all the DNS servers across this great earth to flush their cache and then watch as people begin to resolve your IP to DNS name
The fun never stops.
any more questions, drop me a line