Do I have a graphics card problem?

Sometimes, while scrolling to read my email in OE, blank white boxes appear on the top of my screen covering up the toolbar icons and more. If I pull the scrollbar too quickly the text appears to melt and look garbled. These things also happen when I am using my browser. Is this a graphics card problem or maybe a display adapter problem? I have Win98, 256 MB ram, system resources free 92%, no problems in Device Manager.