function image() { 
}; 

image = new image(); 
number = 0; 

// imageArray 
image[number++] = "<img src='img/headers/MVE_header_01.jpg' border='0' width='758'>" 
image[number++] = "<img src='img/headers/MVE_header_02.jpg' border='0' width='758'>" 
image[number++] = "<img src='img/headers/MVE_header_03.jpg' border='0' width='758'>" 
image[number++] = "<img src='img/headers/MVE_header_04.jpg' border='0' width='758'>" 
image[number++] = "<img src='img/headers/MVE_header_05.jpg' border='0' width='758'>" 
// keep adding items here... 

increment = Math.floor(Math.random() * number); 

document.write(image[increment]);