var selectedBtn = null;
var overRule = /^(.*)\.(\w{3})$/;
var outRule = /^(.*)(_over)\.(\w{3})$/;

var onMouseOver_handler = function()
{
	this.src = this.src.replace( overRule, '$1_over.$2' );
	selectedBtn.src = selectedBtn.src.replace( outRule, '$1.$3' );
}

var onMouseOut_handler = function()
{
	this.src = this.src.replace( outRule, '$1.$3' );
	selectedBtn.src = selectedBtn.src.replace( overRule, '$1_over.$2' );
}

var topnav_handler = function()
{
	var menu = document.getElementById('menu');
	
	if( menu )
	{
		var hrefs = menu.getElementsByTagName('a');
		
		if( hrefs )
		{
			var currentImage = null;
			
			for( var i = 0; i < hrefs.length; i++ )
			{
				if( hrefs[i].firstChild.src.match( /_over/ ) )
				{
					selectedBtn = hrefs[i].firstChild;
				}
			}
			
			for( var i = 0; i < hrefs.length; i++ )
			{
				currentImage = hrefs[i].firstChild;
				
				if( currentImage != selectedBtn )
				{
					currentImage.onmouseover = onMouseOver_handler;
					currentImage.onmouseout = onMouseOut_handler;
				}
			}
		}
	}
}