You can have many resources in one room, but a resource would only be assigned to one room at any one point, for example even a moveable projector would be Room x, then Storeroom, Room Y.
You cannot have something in two places at once
I think that would be come one room to a many resources relationship. As I said its been a long long time since I have done this, so please check my logic in the relevant book/online thing.
I think it might work if you do, resource to room as a one room to many resources, and then has the resource line as part of the meeting? That maintains the many to one relationships.
Easiest way I think when doing these things is to think what is the driver of the change of something. The room has resources, meeting is called, extra resources needed, starts process, changes number of resources in the room through the form!
Cheers,