http and https on same website

Yes, you can run both on the same server, http://www.iisfaq.com/?View=A407&Print=1
Typically you'd make a link to the "Secure" version of the site on the "un-secure" site, BUT with IIS I think you have to have a SECOND IP address to use... remember you need a second IP address for using an SSL (aka httpS) site. A Vhost will not use SSL.

or perhaps look at this answer from EE
http://www.experts-exchange.com/Networking/Microsoft_Network/Q_20773279.html
This little piece of vb code accomplishes both. All you have to do is copy this code into notepad and save it as an asp page in your default directory for the site you're working with, then enable it as the default document. This obviously prevents you from running anything else on the default web site...

<%

     If Request.ServerVariables("SERVER_PORT")=80 or Request.ServerVariables("SERVER_PORT")=443 Then
          Dim strSecureStr
          strSecureURL = "https://"
          strSecureURL = strSecureURL & "mail.domain.com"
          strSecureURL = strSecureURL & "/exchange"
          Response.Redirect strSecureURL
     End If
     %>

This code will basically take anything that comes in on port 80 OR port 443 and redirect it to https:// AND /exchange. If you're not redirecting to a virtual directory you'd just take that line out, and it would redirect anything coming in on 80 or 443 to httpS/.

-rich