var imgArrayHeader = new Array(); 

imgArrayHeader[0] = './images/header/hp_1.gif' 
imgArrayHeader[1] = './images/header/hp_2.gif' 
imgArrayHeader[2] = './images/header/hp_3.gif' 
imgArrayHeader[3] = './images/header/hp_4.gif'
imgArrayHeader[4] = './images/header/hp_5.gif' 
imgArrayHeader[5] = './images/header/hp_6.gif' 
imgArrayHeader[6] = './images/header/hp_7.gif' 
imgArrayHeader[7] = './images/header/hp_8.gif' 
imgArrayHeader[8] = './images/header/hp_9.gif' 
imgArrayHeader[9] = './images/header/hp_10.gif' 
imgArrayHeader[10] = './images/header/hp_11.gif' 
imgArrayHeader[11] = './images/header/hp_12.gif' 
imgArrayHeader[12] = './images/header/hp_13.gif' 
imgArrayHeader[13] = './images/header/hp_14.gif' 

var q = imgArrayHeader.length; 

var newHeaderImage = Math.round(Math.random()*(q-1)); 
function showHeaderImage(){ 
document.write('<img src="'+imgArrayHeader[newHeaderImage]+'">'); 
}