Bitmap display issue

I have numerous Dell Inspiron 3800 laptops running Win98se with ATI rage mobility-m1 agp 2x[english] display adapters. On a few of these machines the only bitmaps that display as wallpaper are the windows system bmps. If I try to add a customized bmp, the only way I can have it show is if I enable active desktop. I have others that do not have the problem at all. Dell support was unable to give me any help except to say enable active desktop. I have looked closely at these systems and can’t see any differece in settings. I welcome all suggestions.