Your server is sending an incorrect content type for the CSS files. Most browsers can handle this, but apparently not IE. Attached is a screen shot using Fiddler. Notice the content type is "text/css,2097151". It should just be "text/css". I don't know how you fix it, but I would start with your IIS configuration settings, especially your MIME type settings.
Roger Martin attached the following image(s):
Roger Martin
Creator and Lead Developer of Gallery Server Pro