if (document.images) {            // Active Images
            img1on = new Image();      
            img1on.src = 'images/navbtn1_on.gif';			
			img1off = new Image();      
            img1off.src = 'images/navbtn1_off.gif';

            img2on = new Image();      
            img2on.src = 'images/navbtn2_on.gif';			
			img2off = new Image();      
            img2off.src = 'images/navbtn2_off.gif';
			
			img3on = new Image();      
            img3on.src = 'images/navbtn3_on.gif';			
			img3off = new Image();      
            img3off.src = 'images/navbtn3_off.gif';
			
	        img4on = new Image();      
            img4on.src = 'images/navbtn4_on.gif';			
			img4off = new Image();      
            img4off.src = 'images/navbtn4_off.gif';
			
			         }

// Function to 'activate' images.
function imgOn(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "on.src");
        }
}

// Function to 'deactivate' images.
function imgOff(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "off.src");
        }
}