Javascript item appearing in Firefox, not IE

I just purchased a Wordpress theme and am customizing it. It uses a
javascript tabbed content area with a script called tabber.js. I'd
already made dozens or hundreds of changes in various templates before
bothering to look at the site in IE7 (always using Firefox 2). The
entire tab area simply doesn't appear in IE. Works fine in Firefox.
Also Safari on a Mac and Opera.

The tabbed area shows up fine in IE at the demo site for the theme.
I've gone over every tag and template hunting for an inconsistency
that could cause this. Something in my code is preventing IE from
running the tabber. Can't imagine it's anything server-side. I've
tried replacing my sidebar.php and a few related templates with the
originals and it still doesn't work in my site. So it's not the code
inside the tabber. Any suggestions?

The page is valid XHTML 1.0 transitional.

My site: http://www.theotherrussia.org (The tab content area appears
under the black and white cartoon on the right sidebar, above the
words "special coverage". You can see it in Firefox...)

Theme demo site: http://www.wp-magazine.com .

Thanks much. Mig

Mig said the following on 12/12/2007 7:27 AM:But it isn't being served to IE as XHTML so it is being handled by IE as
tag soup HTML. IE doesn't have a clue what XHTML is.
I see it just fine in IE7.

--
Randy
Chance Favors The Prepared Mind
comp.lang.javascript FAQ - http://jibbering.com/faq/index.html
Javascript Best Practices - http://www.JavascriptToolbox.com/bestpractices/