iweb address not masking

I recently purchased a domain name at godaddy.com. I set it up to forward to my iweb address and that worked outfine. Next I tried to mask the iweb address so the godaddy address would still show up once they get to the website. This is not working. I did it like the site says. I went to Domain Forwarding then masking and under "Masked Title" i typed my godaddy address; "http://www.godaddyaddress.com. It said to give it a few minutes but once it finished, my site still displayed the iweb address. What am I doing wrong? Any advice? Thanks