Another update. This one features environmental objects (/env_object) like signs. The sign graphic is there on screen, but the actual object is invisible. When a player presses the Action botton (Which in this case is Spacebar) the player calls the Use() proc for all entities in front of said player. terrain graphics (or /turf objects) aren't called, but (/mob) and its derivatives are called.
The sidebar is still kinda iffy, because nothing is updated just yet. I did add a section for a target, with an icon and health bar which will appear soon. The lower-right window was going to be the target section, but was changed to the chat pane, and the chat tab in the tabs shown on the top-left of the screen was removed for simplicity's sake.
The dialog box is another skin control contained in a 'child' object, which displays different panes in the main window. It is not part of the map control itself, but rather overlays the map in such a way that it displays text when you Use() something (if it asks for a dialog box anyway).
I think I'll keep the menu tab as a sort of "pause" tab. In multiplayer, this will not cease play, but it will in singleplayer. The Map tab will do the same thing.