You can't do it from within AutoCAD to my knowledge.
You can however download a program called Quikpik and this has the capacity to lock the toolbars and other floating windows so that you don't accidentally move them (you press CTRL & move to adjust them). This is the main reason why I installed this package but it's other great benefit is that it displays your pull down boxes (eg layer control) as wide as you need it to read it all properly, because you can't stretch these in autocad ...another glaring oversight by autodesk, but made much better by Quikpik.
So it's a good package imo and doesn't cost must to register should you wish to do it, but the shareware doesn't stop working after a certain amount of time, hint hint ;o)