;-) The A2000 is built like a tank. It was meant to sit below the monitor, so there are no worries there. Also, that arrangement allows the two to share the same footprint on the desk, and thus to use less space between them.
Still, if you want to put it on its side, there should be no trouble. I wouldn't recommend it, though; the case wasn't designed that way. Your ports on the left would have to go up top, and thus your floppy drives or the right would be next to the floor, collecting more dust. That's not a good idea.
