gross, but functional

function showBlockingPopup(name) {
  // make sure overlay covers the entire page
  var dimensions = document.viewport.getScrollOffsets();
  wrapper = $(name);
  
  // center logo
  $(name + '_popup').setStyle({top: (dimensions.top + (document.viewport.getHeight() / 2) - 68) + 'px'});
  
  if(Prototype.Browser.IE) {
    var newHeight = Math.max(document.documentElement.scrollHeight, document.documentElement.clientHeight);
    var newWidth = document.documentElement.offsetWidth;
    
    // set height/width on #name and its _blocker, otherwise IE won't let _blocker grow
    wrapper.setStyle({height: newHeight + 'px', width: newWidth + 'px'});
    $(name + '_blocker').setStyle({height: newHeight + 'px', width: newWidth + 'px'});
    
  } else if(Prototype.Browser.WebKit) {
    $(name + '_blocker').setStyle({height: (document.body.scrollHeight > document.body.offsetHeight ? document.body.scrollHeight : document.body.offsetHeight) + 'px'});
  } else {
    $(name + '_blocker').setStyle({height: window.innerHeight + window.scrollMaxY + 'px'});
  }
  
  wrapper.setStyle({zIndex: Number.MAX_VALUE});
  
  if(Prototype.Browser.IE) {
    // setTimeout used so the animated GIF will animate itself
   wrapper.show.delay(.1);
  } else {
   wrapper.show(); 
  }
}