function podImageClass() {

   if ( !(this instanceof podImageClass) ) return new podImageClass();

   var browser;

   var podImage;
   var podImageHeight;
   var podImageWidth;
   var podImageAspect;

   var debounceResize = 0;
   var haveResized = 0;

   function __setViewOriginalLink(displayBool) {
       var voLink = document.getElementById("podImageViewOriginalLink");
       if (displayBool) {
          voLink.innerHTML = 
              '<a href="javascript:podImage.setOriginalSize()">' +
              "Scale to Original Size" + "</a>";
       } else {
          voLink.innerHTML = '&nbsp;';
       }
   }

   function _setText () {
       var podImageText = '"<$MTEntryTitle$>"' + " / " +
           "Click For Previous";
       podImage.alt = podImageText;
       podImage.title = podImageText;
   }

   function _setSize() {
      var myWidth = 0, myHeight = 0;
    
      if (debounceResize) {
         debounceResize = 0;
         return;
      }

      if( typeof( window.innerWidth ) == 'number' ) {
         //Non-IE
         myWidth = window.innerWidth;
         myHeight = window.innerHeight;
      } else if( document.documentElement &&
         ( document.documentElement.clientWidth ||  
            document.documentElement.clientHeight ) ) {
         //IE 6+ in 'standards compliant mode'
         myWidth = document.documentElement.clientWidth;
         myHeight = document.documentElement.clientHeight;
      } else if( document.body && ( document.body.clientWidth || 
            document.body.clientHeight ) ) {
         //IE 4 compatible
         myWidth = document.body.clientWidth;
         myHeight = document.body.clientHeight;
      }

      // Only do the resize if we've done this before or if our
      // image is greater than their window size 64px of top margin.
      if ( !( haveResized || ((podImageHeight + 64) > myHeight) ) ) {
         return;
      }

      // allow 128px margins on top and bottom:
      var newImageHeight = myHeight - ( 2 * 128 );

      if ( (podImageHeight + 64) < myHeight ) {
         // Just use original width and height;
         _setOriginalSize();
      } else {
         // Downscale:
         if (newImageHeight > 0) {
            var newImageWidth = newImageHeight * podImageAspect;
            podImage.width = newImageWidth;
            podImage.height = newImageHeight;
         }

         __setViewOriginalLink(true);
      }

      haveResized = 1;
   }

   function _setOriginalSize() {
      // We have to play with the onresize handler to work
      // around IE sending spurious events.
      window.onresize = null;
      podImage.width = podImageWidth;
      podImage.height = podImageHeight;
      __setViewOriginalLink(false);
      if (browser == "MSIE") {
         debounceResize = 1;
      }
      window.onresize = _setSize;
   }

   function _checkIt(string)
   {
      var detect = navigator.userAgent.toLowerCase();
      place = detect.indexOf(string) + 1;
      thestring = string;
      return place;
   }

   function _init() {
      if (_checkIt('msie')) browser = "MSIE"
      else browser = "Other";

      podImage = document.getElementById("podImage");
      podImageWidth = podImage.width;
      podImageHeight = podImage.height;
      podImageAspect = (podImageHeight > 0) ?
         (podImageWidth / podImageHeight) : 0;
   }

   this.init = _init;
   this.setText = _setText;
   this.setSize = _setSize;
   this.setOriginalSize = _setOriginalSize;

   _init();
}

<!-- setup podImage class: -->
var podImage;
addLoadEvent(function() {
        podImage = podImageClass();
        podImage.setText();
        podImage.setSize();
        window.onresize = podImage.setSize;
});

It's live on the site now; let me know if you run into any bugs or if you just find the whole thing annoying.

I'm sure one day this entire exercise will be reduced to two lines of CSS.