This is giving me fits too. I found a few useful resources - MS Knowledge Base Article 291616, and an older Technet article titled "How to Set Up a Conference Room as a "Resource" in Outlook 2000". However, I've been unable to get the conference room's availability to show. I'm currently working with Office online support on this issue
Anyway, check out these resources if you haven't already. Maybe you'll have better luck than I've had.