Because you're working in 3D, a simple magnify isn't all that simple... The answer is to use your cameras, and learn the hot-keys for them so you can switch quickly while you're working. ProPack has a multi-pane view, but that won't be much use at 800x600. I usually set up my Main camera (ctrl-M) to cover the final composition, and set render preferences to render to a new window if it's going to be bigger than the document window. Then navigate around the scene with the other cameras - you can set up the posing, aux and dolly cameras to point to key areas, and of course adjust them to see what you want to see. Not all have hot-keys, frustratingly. When I'm composing a scene, sometimes every other action is a camera related one.