If you are on a dynamic IP you'll need to use a service such as http://www.no-ip.com/ which is a Dynamic DNS service. It'll keep track of your IP address updating it's DNS accordingly to route traffic to your local WAMP server when people type in your website address. So once you sign up with them or any other service go to whatismyip.com get your IP address and enter it along with the website to point it to. You'll probably have to update the name servers in the registrar to point to the DNS service provider.
You'll need to make sure port 80 is open some ISP's block this unless you have a higher class of service so check with them. Then login to your router and route port 80 to the local IP of the computer with WAMP installed on.
You can even have another computer on your network running WAMP and in the router just set the IP to route to.