You have to do some more steps..
1. Configure your modem, so that it supports NAT and points to your computer.
(where the server is running)
2. If you are successful in the first step, you should be able to access ur site from external world like this
http://123.123.123.123 (ur ip)
3. If u see this... better go to
http://www.dyndns.org and register a free domain name... it will be something like this
http://urname.dyndns.org
You should loging to dynns and configure ur ip address there... You have to explore things... (if ur still lazy.... use their DynDNS update client.. it will take care of things... in which u r lazy...)
4. If you are successful, (mmm??) You can think about obtaining ur own original website name... goto
http://www.godaddy.com or any hosting provider and register a domain name with them....
5. Then point that domain name to your IP address...
(I think you will be getting back to me within these steps... lets continue if u still need help)
regards