adding conference rooms as "resources" in active directory/Exchange for scheduling

I had somebody ask me the following question:

"we used shared calendars in Outlook and somebody suggested we set the conference rooms up so we can schedule them. They said to add them as resources in active directory/exchange instead of as users and then you can schedule them. How do we do that?"

To which I replied, "I'll find out".

Can somebody help me "find out"?

Thanks