Thanks for the welcome!
I'm using AutoCAD MEP 2011 and managed code. I believe that MEP also includes everything in AutoCAD Architecture (and vice versa).
A "space" is a an entity that is used to display information about a room within a floor plan. Basically, the space feature allows you to analyze a floor plan of lines and walls and determine where the rooms are. It will attempt to trace features such as walls and windows, giving you a polygon for each room. It's useful for HVAC because it can give things such as floor area, exterior wall and window areas, and other information that is useful for heating and cooling load calcs.
Tracing a room with a polyline and filling it with a hatch is essentially what a space looks like, although I'm not entirely sure exactly how its shape is stored in the dwg database. But I think it should be relatively easy to get its geometry and then find all entities within that geometry.