if you forward port 80 to your ip only, i think the other computer in your network won't be able to access the web
btw check out this page for a list of commonly used ports, maybe it'll help you out
Practically Network's port list
i don't know about dns2go, i'm usind no-ip. but i think they're sort of similar. just run you client (after you've registered your dns name) and you're ready to run. what you need to make sure is that you've opened the right ports in your router's config.
if you're still having problems, post em here...
cheers