if (document.images) 
{ 
nav1on = new Image();
nav1on.src = "images/nav_home_on.gif";
nav2on = new Image();
nav2on.src = "images/nav_books_on.gif";
nav3on = new Image();
nav3on.src = "images/nav_science_on.gif";
nav4on = new Image();
nav4on.src = "images/nav_art_on.gif";
nav5on = new Image();
nav5on.src = "images/nav_bio_on.gif";
nav6on = new Image();
nav6on.src = "images/nav_contact_on.gif";
nav7on = new Image();
nav7on.src = "images/nav_events_on.gif";

nav1off = new Image();
nav1off.src = "images/nav_home_off.gif";
nav2off = new Image();
nav2off.src = "images/nav_books_off.gif";
nav3off = new Image();
nav3off.src = "images/nav_science_off.gif";
nav4off = new Image();
nav4off.src = "images/nav_art_off.gif";
nav5off = new Image();
nav5off.src = "images/nav_bio_off.gif";
nav6off = new Image();
nav6off.src = "images/nav_contact_off.gif";
nav7off = new Image();
nav7off.src = "images/nav_events_off.gif";
} 

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

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


function imgNav(imgName, NavNo)
{
if (document.images)
{ document[imgName].src = "images/" + NavNo + "_navpic.jpg";
}
}