help with transition effect for a VERY simple small gallery

help with transition effect for a VERY simple small gallery

I'm working on a very simple gallery for a site I'm building which consists of four thumbnails and 1 large view image.

At the moment, when a user hovers the thumbnail, the large view image changes to the image in the thumbnail.

I'm new to jquery and I was hoping someone could help me out getting a nice transition effect, ie - when a user hovers a thumbnail, the large view image fades in over the existing one rather than the immedite switch currently happening.

JS is
$(document).ready(function(){
   
   $(".preview").hover(function() {

      $("#WZ1left").html('<img src="'+ this.href +'" alt="test" height="356" width="356" />');
      $("#WZ1left").fadeIn("slow");
   
   });
   
});