What Daniel ment was the text at the footer of JoomlaComment - "Powered by Rocky Mountain Raider:Adventures". There's nothing wrong with you doing that, but it just means that the comment.class.php file has been modified.
<link href="/index.php?option=com_bca-rss-syndicator&feed_id=1" rel="alternate" type="application/rss+xml" title="RRR" />
Hmm. Is this the standard Joomla RSS feed link, or from a third party component? (Do you recognize that Daniel?). As I discovered with bugfixing the RSD plugin, the AJAX in JoomlaComment does conflict with custom xml head feeds. Perhaps you could try disabling this "com_bca-rss-syndicator" component and testing the Comment system again. It would explain why only IE users are able to comment, because IE6 ignores most of these head links as far as I know.
Also, I noticed you are using the great module from Gavik called "News Pro GK1", and it's JavaScript library
could be conflicting with the AJAX. So also try testing a comment with that module unpublished.
Either way, i'm very interested to get to the bottom of this - we havn't given up yet! Because when we do find the reason, of course that's another possible bug we can investigate and fix