Takéto niečo?

<form method="get" action="">
Počet obrázků : <input id="count" size="2" maxlength="2"> (max.: 6)
<div id="inputs"></div>
<div id="images"></div>
<input id="submit" type="submit" />
</form>
<script>
var count = document.getElementById('count');
var inputs = document.getElementById('inputs');
var images = document.getElementById('images');
var bindInput = function(input, fn) {
	input.oninput = function(e) {
		this.onkeydown = null;
		fn.call(this, e);
	};
	input.onkeydown = function(e) {
		fn.call(this, e);
	};
};
var onInput = function(e) {
	e = e || window.event;
	var target = e.target || e.srcElement;
	if (target.timer) {
		clearTimeout(target.timer);
		target.timer = null;
	}
	for (var input = inputs.firstChild, i = 0; input; input = input.nextSibling, ++i)
		if (input == target) {
			target.timer = setTimeout(function() {
				images.childNodes[i].src = target.value;
				target.timer = null;
			}, 500);
			break;
		}
};
var onCountInput = function(e) {
	var count = Math.max(1, Math.min(6, this.value));
	if (isNaN(count))
		count = 1;
	var actual = inputs.childNodes.length;
	while (count < actual--) {
		inputs.removeChild(inputs.lastChild);
		images.removeChild(images.lastChild);
	}
	while (++actual < count) {
		var input = document.createElement('input');
		input.name = 'cislo' + (actual + 1);
		bindInput(input, onInput);
		inputs.appendChild(input);
		var image = new Image();
		images.appendChild(image);
	}
}
bindInput(count, onCountInput);
onCountInput.call(count);
</script>