Publishing A Site using ISA Server

We are currently publishing a website to the internet thru our ISA (microsoft’s new firewall and proxy software) server. After a bit of configurations, we finally published the homepage (default). The problem is when we are going to log-in (now using SSL (HTTPS)) to the site, error occurs. I’ve already opened port 80(http) and 443(https), still i got “page cannot be displayed” errors). How to I fix this? Does it need certficates for ssl tunneling? Help me please. Please include procedures. Thanks.