function rnd(algus, lopp) { return Math.round((Math.random() * (lopp-algus)) + algus); }
function set_taust()
{
	var
		pilt = '../images/taust.gif',
		obj  = document.body,
		pilt_height = 300, pilt_width  = 300,
		hoia_top = 0, hoia_bott = 0, hoia_right = 0, hoia_left = 0;

	l = rnd(hoia_left, obj.clientWidth  - pilt_width  - hoia_right);
	t = rnd(hoia_top,  obj.clientHeight - pilt_height - hoia_bott );
	obj.style.backgroundImage = 'url(' + pilt + ')';
	obj.style.backgroundPosition  = l + 'px ' + t + 'px';
}