/*
	rollover function
	
	usage: <a href="#" onmouseover="rollover(this)" onmouseout="rollover(this)"><img src=""/></a>
	
	rollover "ON" images should always be in the form filename_h.ext
	(if the "OFF" images are of the form filename.ext)
*/
function rollover(a)
{
	// get all image tags inside the link
	var img = a.getElementsByTagName('img');
	if(!img) return;
	
	// only use the first occurence
	img = img.item(0);
	
	// store original link
	if(!img.org_src) img.org_src = (img.style.filter ? img.style.filter : img.src);
	
	// get extension of file
	var ext = img.org_src.split('.');
	ext = ext[ext.length-1];
	
	// if original file already had the rollover image ("_h"), then don't rollover at all
	if(img.org_src.indexOf('_h.' + ext) > -1) return;
	
	// apply the rollover (IE6)
	if(img.style.filter)
	{
		if(img.style.filter.indexOf('_h.' + ext) > -1)
		{
			img.style.filter = img.style.filter.replace('_h.' + ext, '.' + ext);
		}
		else
		{
			img.style.filter = img.style.filter.replace('.' + ext, '_h.' + ext);
		}
	}
	// apply the rollover (all other browsers)
	else
	{
		if(img.src.indexOf('_h.' + ext) > -1)
		{
			img.src = img.src.replace('_h.' + ext, '.' + ext);
		}
		else
		{
			img.src = img.src.replace('.' + ext, '_h.' + ext);
		}
	}
}