Changing HTTP default to HTTPS - IIS 5

I have sucessfully installed and configured an SSL site on IIS 5. However, when I enter www.mycompany.com into a browser, the site defaults to http://www.mycompany.com rather than https://www.mycompany.com. Naturally, I receive the default error "you are trying to access an SSL site, etc etc." (If I manualy put in https:// the site works perfectly). Is there a way to tell IIS 5 to use https:// as the default HTTP 'header'?

I may have overlooked a simple step here....
Thanks for any help!