// Set source images
var navImagesSource = [
	['../images/bt_nav_download_OFF.gif','../images/bt_nav_download_ON.gif'],
	['../images/bt_nav_about_OFF.gif','../images/bt_nav_about_ON.gif'],
	['../images/bt_nav_nrpc_members_OFF.gif','../images/bt_nav_nrpc_members_ON.gif'],
	['../images/bt_nav_contact_OFF.gif','../images/bt_nav_contact_ON.gif']
];
var navImages = [];

// Preload images
for(var i = 0; i < navImagesSource.length; i++){
	navImages[i] = [];
	navImages[i][0] = new Image();
	navImages[i][0].src = navImagesSource[i][0];
	navImages[i][1] = new Image();
	navImages[i][1].src = navImagesSource[i][1];
}

function navRollover(id,state){
	document.images['nav' + id].src = navImages[id][state].src;
}