var im_pre = new Array;
var cur_imgid = '';
var cur_saved = '';

function preload(id, src) {
	im_pre[id] = new Image();
	im_pre[id].src = src;
}

function unswap() {
	if (('' != cur_imgid) && ('' != cur_saved)) {
	document.images[cur_imgid].src = cur_saved;
	cur_imgid='';
	cur_saved='';
	}
}

function swap(imgid) {
	unswap();
	cur_imgid = imgid;
	cur_saved = document.images[imgid].src;
	document.images[imgid].src = im_pre[imgid].src;
}