Connecting to Exchange Server Over HTTP

Greetings,

I started following some instructions on how to get Outlook to connect to Exchange Server 2003 over HTTP, and when I got to the point in the "More Settings" area of the Exchange Server Mailbox setup where I did not see the checkbox I was supposed to on the "Connection" tab. Apparently there's supposed to be one that says "Connect to my Exchange mailbox using HTTP" but I don't see that - instead it's just empty space.

Funny thing is, I do see that on my laptop's Outlook so it works fine on that computer. Does anyone know why I'm not seeing these options on my desktop machine?