i haven't read the links that tez posted (and i have been out drinking tonight so please excuse the bad posting)
Use a service such as
www.no-ip.com or
www.dyndns.org to make sure that your domain always forwards to your public ip address.
Then you need to make sure that your router forwards the ports to the machine that you are using. Alternatively you can put the webserver in the DMZ if this option is available on your router, although i woudln't recommend this as it means your webserver would have no hardware firewall protection. DMZ = Demilatratilzes Zone
MB