var Masts = new Array(4);
Masts[0]='Invesco.jpg';
Masts[1]='Hughes.jpg';
Masts[2]='HalfFront.jpg';
Masts[3]='Patriotic.jpg';
Masts[4]='PreGame.jpg';
Masts[5]='Curls.jpg';

function RandomMast() {
var intNum=NaN;
while (isNaN(intNum)) {
intNum=Math.floor(Math.random()*(Masts.length));
}

document.write('<img src="Media/Masts/'+Masts[intNum]+'" width="320" height="84" alt="Mast">');
}