That's bizzare. Sounds like something got messed up with your file extensions in Windows. I'm not even sure how to fix that offhand. Go to Tools/Folder Options in an Explorer window and check under the File Types tab for anything that relates to Windows Explorer. I don't even know what to do there, but that's where I'd start looking for some sort of problem. I'm running Win2K, so I can't check for you, and it's been awhile since I used Win98.
A really quick way of opening Explorer, however, if you're looking for a new method, is Windows key + E.