Your images don't show up in Mozilla Firebird either. I suggest using ONE stylesheet (or maybe 2, one for older browsers that gets <link>ed, and another for newer browsers that gets @import'ed and overrides the styles in the <link>ed stylesheet) and foregoing the browser/user agent string checks. If you're going to use this message:
Then you should be using proper Web standards as well.
<p class="browsernote"><big>This site's design is only visible in a graphical browser that supports <a href="http://www.webstandards.org/upgrade/" title="The
Web Standards Project's BROWSER UPGRADE
initiative.">web standards</a>, but its content is
accessible to any browser or Internet device.</big></p>