ARR Newbie - ARR isn't forwarding

So I created a new 2008 VM, installed IIS7, and installed ARR 2.5.

I have an existing IIS6 webserver on a different VM that hosts about 10 sites using host headers. Right now, my firewall redirects all http requests to this VM. I pointed it to the ARR server.

I added a server farm to ARR, and I added the names of the subdomains I wanted to be sent to the existing IIS6:
site1.contoso.com, site2.contoso.com, etc.

Now I can't get to these sites. The documentation on the site doesn't seem to address this simple redirection problem, or I probably can't find it. Can someone help?