Dreamweaver Image Swap Beh'vior Fails in IE

I recently made a gallery site for an artist that utilizes DW's image swapping
behavior to swap images in the gallery -- click on the thumbnail, the larger
image is swapped. Works fine on my Mac, on other people's -- Safari, Mozilla,
NN, IE 5.5 -- but on some versions of IE, esp on PC's, it fails: the image
won't swap properly. See

http://www.benpritchard.com/gallery/index2.htm


Someone suggested preloading the images -- I've tried this on the "home" page
for the gallery for the moment -- but the images are fairly large and I'd
rather avoid this. Can anyone help give me a definitive answer why the DW
swapping code fails in IE (sometimes!)? I'd appreciate it, as I need to
resolve the issue so my client's happy. --

Thanks very much for any help!