The tabs do not show the CSS rollover in MSIE. With the behavior "csshover.htc" MSIE behaves as the other browsers. I added the code to load this behavior via CSS to "javascript.php", because I think this is the best place to handle the behavioral layer of moodle. Perhaps it makes sense to rename it to "behavior.php"???

lib/csshover.htc

@@ -0,0 +1,88 @@
+<attach event="ondocumentready" handler="parseStylesheets" />
+<script language="JScript">
+/**
+ *	PSUEDOS - V1.21.041022 - hover & active
+ *	---------------------------------------------
+ *	Peterned - http://www.xs4all.nl/~peterned/
+ *	(c) 2004 - Peter Nederlof
+ *
+ *	Credits  - Arnoud Berendsen 
+ *	         - Martin Reurings
+ *	for inspiring me and finding really sick bugs
+ *
+ *	howto: body { behavior:url("csshover.htc"); }
+ *	---------------------------------------------
+ */
+
+var currentSheet, doc = window.document;
+var activators = {
+	onhover:{on:'onmouseover', off:'onmouseout'},
+	onactive:{on:'onmousedown', off:'onmouseup'}
+}
+
+function parseStylesheets() {
+	var sheets = doc.styleSheets, l = sheets.length;
+	for(var i=0; i<l; i++) 
+		parseStylesheet(sheets[i]);
+}
+	function parseStylesheet(sheet) {
+		var l, rules, imports;
+		if(sheet.imports) {
+			imports = sheet.imports, l = imports.length;
+			for(var i=0; i<l; i++) 
+				parseStylesheet(sheet.imports[i]);
+		}
+
+		rules = (currentSheet = sheet).rules, l = rules.length;
+		for(var j=0; j<l; j++) parseCSSRule(rules[j]);
+	}
+
+	function parseCSSRule(rule) {
+		var select = rule.selectorText, style = rule.style.cssText;
+		if(!(/(^|\s)(([^a]([^ ]+)?)|(a([^#.][^ ]+)+)):(hover|active)/i).test(select) || !style) return;
+		
+		var pseudo = select.replace(/[^:]+:([a-z-]+).*/i, 'on$1');
+		var newSelect = select.replace(/(\.([a-z0-9_-]+):[a-z]+)|(:[a-z]+)/gi, '.$2' + pseudo);
+		var className = (/\.([a-z0-9_-]*on(hover|active))/i).exec(newSelect)[1];
+		var affected = select.replace(/:hover.*$/, '');
+		var elements = getElementsBySelect(affected);
+
+		currentSheet.addRule(newSelect, style);
+		for(var i=0; i<elements.length; i++)
+			new HoverElement(elements[i], className, activators[pseudo]);
+	}
+
+function HoverElement(node, className, events) {
+	if(!node.hovers) node.hovers = {};
+	if(node.hovers[className]) return;
+	node.hovers[className] = true;
+	node.attachEvent(events.on,
+		function() { node.className += ' ' + className; });
+	node.attachEvent(events.off,
+		function() { node.className = 
+			node.className.replace(new RegExp('\\s+'+className, 'g'),''); });
+}
+
+function getElementsBySelect(rule) {
+	var parts, nodes = [doc];
+	parts = rule.split(' ');
+	for(var i=0; i<parts.length; i++) {
+		nodes = getSelectedNodes(parts[i], nodes);
+	}	return nodes;
+}
+	function getSelectedNodes(select, elements) {
+		var result, node, nodes = [];
+		var classname = (/\.([a-z0-9_-]+)/i).exec(select);
+		var identify = (/\#([a-z0-9_-]+)/i).exec(select);
+		var tagName = (/^[a-z0-9]+/i).exec(select.toUpperCase()) || '*';
+		for(var i=0; i<elements.length; i++) {
+			result = elements[i].getElementsByTagName(tagName);
+			for(var j=0; j<result.length; j++) {
+				node = result[j];
+				if((identify && node.id != identify[1]) || (classname && !(new RegExp('\\b' +
+					classname[1] + '\\b').exec(node.className)))) continue;
+				nodes[nodes.length] = node;
+			}
+		}	return nodes;
+	}
+</script>

lib/javascript.php

@@ -9,6 +9,8 @@
         echo '<script language="JavaScript" type="text/javascript" src="'.$CFG->wwwroot.'/lib/speller/spellChecker.js"></script>'."\n";
     }
 ?>
+<style type="text/css">/*<![CDATA[*/ body{behavior:url(<?php echo $CFG->wwwroot ?>/lib/csshover.htc);} /*]]>*/</style>
+
 <script language="JavaScript" type="text/javascript" src="<?php echo $CFG->wwwroot ?>/lib/javascript-static.js"></script>
 <script language="JavaScript" type="text/javascript" src="<?php echo $CFG->wwwroot ?>/lib/javascript-mod.php"></script>
 <script language="JavaScript" type="text/javascript" src="<?php echo $CFG->wwwroot ?>/lib/overlib.js"></script>