IE DOM woes

This code works fine in Gecko browsers, but IE doesn’t seem to want to
actuate the onclick handler:

http://colliertech.org/~cjcollier/cadmiumyellow/portfolio/index.php?section=02_free_lance
(usually opened by clicking on one of the rollover images on this page)
http://colliertech.org/~cjcollier/cadmiumyellow/portfolio.html

The bit that seems to work in Gecko but not IE is this:

<a href="#" onclick="advance_view(52);">
<img id="arrow_right" class="imgover" src="images/Arrow_r.gif" alt="Right Arrow" />
</a>

Specifically the onclick handler. I tried putting an alert(‘hi’) in the
handler, but it never pops up in IE. Do you think this has something to
do with how the arrow obscures another image that also has an onclick
handler? The other one doesn’t fire either, though. As a matter of
fact, none of them do in IE, but they all do in Gecko.

The javascript file that defines these handlers is here:

http://colliertech.org/~cjcollier/cadmiumyellow/portfolio/js/portfolio.js

Thanks in advance for any help you can provide