I click save changes and I tested the link :
http://lost.webhop.net/~jelvischan1
It works for me and my dad's machine, but this could be only for my local network.
I am really perplexed when it comes to forward port 80, and I really don't want to mess with the internet modem. Is that the only way?!? I was soooo close.
Yes, this is the only way to get web traffic onto your computer from outside your home network.
What's happening is that your DynDNS account is set up correctly, so when I access your DynDNS weblink (lost.webhop.net), the DynDNS server gives me the IP address which your router is using to connect to the internet. So we're knocking on your door, in a virtual sense, and awaiting an answer...
But your router is also a firewall, and by default it is set to ignore all incoming requests. So our browsers sit, requesting, and hear nothing back. Your browser, and your dad's browser, work because the router is smart enough to see that they're both already inside the firewall.
By forwarding port 80 you are telling your router "it's ok, I'm expecting people to send incoming web requests, because I'm running a web server on one of my computers, and here is where you should send those requests to. Please continue to block everything else, but allow web requests to come in."
It's like telling everyone your address to come visit you, but the security guard at the door is refusing to answer the door when people knock. You have to tell the guard that you're expecting certain people, and when they knock, please escort them to the right room in your house.
The only other way to do this is to buy a web hosting package, one that lets you run PHP scripts, and run everything off one of their servers. (99% of web hosts provide PHP -- unfortunately iWeb/MobileMe falls into the 1% that don't). You upload your script to their server, link to their server, and let them take care of it. This way nobody even has to know anything about where your computer lives on the 'net. Of course, this does cost money, all the way from "free" (usually with catches, like ads) to between $3-30 per month. Personally I'm a fan of DreamHost.