If I understand you right, the sides and/or top of the viewable area of your monitor distort when you open or close any window?
If this is the case, I had this problem once with my monitor and a Radeon card. Although everything works fine, it is a hardware incompatibilty issue. Some videocards allow refresh rates that the monitor isnt designed to handle. In my case I had inadvertantly selected a refresh rate that my monitor was having problems with.
There is a setting under your monitor properties tab that allows or disallows you to select refresh rates that your monitor supports. By unchecking the box, you are allowed to select any refresh rate that the video card can support. The monitor may not be able to support that setting, and in turn can cause erratic display or even damage the monitor and/or video card. In my case, I was lucky...I rechecked the box and set the rate. This cured all my monitor grief.
Im not sure if this even applies to what you are describing, but it sounded vaguely familiar to the problem I had...
I cant remember if 98 has this setting or not. I dont have a 98 machine anymore to check it on. I do know that XP (home and pro) both have this option.
later...