Do you have a .mac page or publishing the iweb page to a godaddy hosted acct? To fwd a domain, you login to godaddy.com homepage, select Domans > My Domains. On the list, check the domain name and click the Forward icon on the tool bar. Put in the full URL of the .mac
You have a godaddy server acct you just want to upload your iweb website to. Use a ftp client, I use Cyberduck. the addess is ftp.nickhiance.com
and put in your username and password you have setup for your website (different than your GD login). Upload all the fies for the site (iweb stores them in your ~/sites I think). Make sure the index.htm is at the ROOT of the acct. This should just take off running at this point, once the files are uploaded.
Hosting acct not linked to your GD URL? Again, while logged into godaddy, select the Hosting & services > My hosting acct. There should be a list of hosting accts with an assigned URL to them. If not, there should be a yellow box that says something about using a credit to setup a page. click the Use Credit link and follow the setup. If the URL is wrong, click OPEN to the right, it's listed in a column called Control Panel. This opens a new window with a stack of options. Click settings > change domain name. Select your URL form the drop down and contine saving the change.