Trouble forcing redirect to HTTPS

I have a site in two zones, default and extranet. They're being served via IPs on two different servers with IIS 7.5, one internal and the other external. I'd like them to work as:

• http://site.internaldomain.com
• https://site.externaldomain.com

I've set up the IP on 443 and SSL cert  to the external site on the external WFE, same as I did in MOSS. I tried creating a new IIS site sharing the same IP to redirect to the https:// prefix, but I'm able to hithttp://site.externaldomain.com. When I'm in IIS, I only see a Browse option of the https site.

I'm missing something here, not sure what it is. Is there an official whitepaper to accomplish what I'm trying to do?

Thanks,

Scott