máscara de moeda no campo

Olá pessoal,

Eu estou tentando digitar os números em real R$ nos campos do formulário só que a formatação, a máscara não sai correto, por que?

Alguém sabe como digitar e ir aparecendo as virgulas em moedas?

<script type="text/javascript">
addEvent = function(o, e, f, s) {
 var r = o[r = "_" + (e = "on" + e)] = o[r] || (o[e] ? [[o[e], o]] : []), a, c, d;
 r[r.length] = [f, s || o], o[e] = function(e){
 try{
 (e = e || event).preventDefault || (e.preventDefault = function(){e.returnValue = false;});
 e.stopPropagation || (e.stopPropagation = function(){e.cancelBubble = true;});
 e.target || (e.target = e.srcElement || null);
 e.key = (e.which + 1 || e.keyCode + 1) - 1 || 0;
 }catch(f){}
 for(d = 1, f = r.length; f; r[--f] && (a = r[f][0], o = r[f][1], a.call ? c = a.call(o, e) : (o._ = a, c = o._(e), o._ = null), d &= c !== false));
 return e = null, !!d;
	}
};

function formatCurrency(o, n, dig, dec) {
 o.c = !isNaN(n) ? Math.abs(n) : 2;
 o.dec = typeof dec != "string" ? "," : dec, o.dig = typeof dig != "string" ? "." : dig;
 addEvent(o, "keypress", function(e) {
 if (e.key > 47 && e.key < 58) {
 var o, s, l = (s = ((o = this).value.replace(/^0+/g, "") + String.fromCharCode(e.key)).replace(/\D/g, "")).length, n;
 if(o.maxLength + 1 && l >= o.maxLength) return false;
 l <= (n = o.c) && (s = new Array(n - l + 2).join("0") + s);
 for(var i = (l = (s = s.split("")).length) - n; (i -= 3) > 0; s[i - 1] += o.dig);
 n && n < l && (s[l - ++n] += o.dec);
 o.value = s.join("");
 }
 e.key > 30 && e.preventDefault();
 });
}

function fmtMoney(n, c, d, t){
 var m = (c = Math.abs(c) + 1 ? c : 2, d = d || ",", t = t || ".",
 /(\d+)(?:(\.\d+)|)/.exec(n + "")), x = m[1].length > 3 ? m[1].length % 3 : 0;
 return (x ? m[1].substr(0, x) + t : "") + m[1].substr(x).replace(/(\d{3})(?=\d)/g,
 "$1" + t) + (c ? d + (+m[2] || 0).toFixed(c).substr(2) : "");
};

function soma() {
 var f = document.forms[0];
 var valor1 = parseFloat(f.campo1.value.replace('.','').replace(',','.'));
 var valor2 = parseFloat(f.campo2.value.replace('.','').replace(',','.'));
 var valor3 = ('' + ((valor1||0) + (valor2||0)));
 f.campo3.value = fmtMoney(valor3);
}

function init() {
 formatCurrency(document.forms[0].campo1, 2, ".", ",");
 formatCurrency(document.forms[0].campo2, 2, ".", ",");
}

</script>

<form>
 <input name="campo1" onkeyup="init();" size="20" /> +
 <input name="campo2" onkeyup="init();" size="20" /> =
 <input name="campo3" size="20" />
</form>