BTW, yarp, can't remember what they call it now but there are two window modes that GIMP can run in. If your GIMP has a separate toolbox and image editing window, you need to get out of that mode but like I said, I cannot remember what it is called now. It's an option either in the menu or preferences, and when you change it, GIMP will behave more like a regular program with all the palettes and toolboxes contained within one big window.

I always use GIMP in a single window and double-click on the titlebar to maximise it.