IE may just not be able to display them. In school we were taught about different issues like that, though I don't recall that being mentioned. That may be because virtually nobody (in my field of graphic/web design anyway) uses .bmp and almost everything is .png or .jpg. Older versions of IE can't display .png either. I recommend using either Firefox or Safari, and yes, despite it being Mac's browser, there is a version of Safari for PC.