var theImages = new Array();

theImages[0] = 'img/floorSidebar1.jpg'
theImages[1] = 'img/floorSidebar2.jpg'
theImages[2] = 'img/floorSidebar3.jpg'

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));
function showImage(id){
	eval("document." + id + ".src = '" + theImages[whichImage] + "'");
}

showImage('floorSidebar');