img1_on = new Image;
		img1_off = new Image;
		img1_on.src = "img/nav/cycling_on.gif";
		img1_off.src = "img/nav/cycling.gif";
		
		img2_on = new Image;
		img2_off = new Image;
		img2_on.src = "img/nav/running_on.gif";
		img2_off.src = "img/nav/running.gif";
		
		img3_on = new Image;
		img3_off = new Image;
		img3_on.src = "img/nav/weight_training_on.gif";
		img3_off.src = "img/nav/weight_training.gif";
		
		img4_on = new Image;
		img4_off = new Image;
		img4_on.src = "img/nav/win_your_guide_on.gif";
		img4_off.src = "img/nav/win_your_guide.gif";	
		
		function swapImg(imgField,newImg)	{
		
			document[imgField].src = eval(newImg+".src")
			
			}