Create a hostname and set your IP to the IP given to you by your ISP (should be automatic).

ENGADGET: How-To Hacks finalist: How to set up your own PSP web portal

Enter your DynamicDNS hostname as the proxy and port 8080 as the...port.

ENGADGET: How-To Hacks finalist: How to set up your own PSP web portal

This is much better than using the DNS trick because you can have the DynDNS IP automatically updated and the hostname won't change.

ENGADGET: How-To Hacks finalist: How to set up your own PSP web portal