var theImagesF = new Array()

theImagesF[0] = 'thumbs/F1.gif'
theImagesF[1] = 'thumbs/F2.gif'
theImagesF[2] = 'thumbs/F3.gif'
theImagesF[3] = 'thumbs/F4.gif'
theImagesF[4] = 'thumbs/F5.gif'
theImagesF[5] = 'thumbs/F6.gif'
theImagesF[6] = 'thumbs/F7.gif'

var j = 0
var p = theImagesF.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImagesF[i]
}
var whichImageF = Math.round(Math.random()*(p-1));
function showImageF(){
document.write('<img src="'+theImagesF[whichImageF]+'">');
}