Did you change DPI settings in Windows? That usually reeks havoc on software.
800x600 could also be a problem. It may be best to run your monitor's normal resolution and use the zoom feature in the browser when needed.
I would highly recommend getting an LED or LCD monitor if at all possible for three reasons: crisper display and a size upgrade for far easier reading and operating cost: LxD monitors consume about 1/3 the power of CRTs and generate less heat.