if (document.images) 
{

nav1on = new Image();
nav1on.src = "images/btn_home_on.gif";
nav1off = new Image();
nav1off.src = "images/btn_home_off.gif";

nav2on = new Image();
nav2on.src = "images/btn_ports_on.gif";
nav2off = new Image();
nav2off.src = "images/btn_ports_off.gif";

nav3on = new Image();
nav3on.src = "images/btn_about_on.gif";
nav3off = new Image();
nav3off.src = "images/btn_about_off.gif";

nav4on = new Image();
nav4on.src = "images/btn_business_on.gif";
nav4off = new Image();
nav4off.src = "images/btn_business_off.gif";

nav5on = new Image();
nav5on.src = "images/btn_links_on.gif";
nav5off = new Image();
nav5off.src = "images/btn_links_off.gif";

nav6on = new Image();
nav6on.src = "images/btn_contact_on.gif";
nav6off = new Image();
nav6off.src = "images/btn_contact_off.gif";

function twinOn(imageName1)  {
	document[imageName1].src=eval(imageName1+"on.src");
	}
 
function twinOff(imageName1,imageName2) {
	document[imageName1].src=eval(imageName1+"off.src");
	}	

}