in iis cp find the folder secure, slect ssl settings from the mail window, and tick "require https", they will now be forced to use https for that folder.
Next if you haven't already, using web platform installer, install url rewrite in IIS, best grab SEO toolkit while you are there. Restart IIS cp after install
Select the site then go to url rewrite,
click add rule
Select blank rule
fill in as per screen shots here
http://screencast.com/t/6qUxduZ7UxWz
http://screencast.com/t/cvivbdFsm
If any problems get back to me. I did this without testing.
If you installed seo toolkit also, you will see there are some ready built rules at bottom, see tutorials here if needed.http://thatsit.com.au/seo/tutorials
Note with the rule remove append trailing slash, I always select remove as when people type out your url they never put a slash on the end.
When your done select the site again and have a play with the SEO toolkit, do a scan on your site.
let me know how you went