Format Brazilian Money

function FormataReais(fld, milSep, decSep, e) {
		var sep = 0;
		var key = '';
		var i = j = 0;
		var len = len2 = 0;
		var strCheck = '0123456789';
		var aux = aux2 = '';
		var whichCode = (window.Event) ? e.which : e.keyCode;
		if (whichCode == 13) return true;
	 	key = String.fromCharCode(whichCode);  // Valor para o código da Chave
		if (strCheck.indexOf(key) == -1) return false;  // Chave inválida
		len = fld.value.length;
		for(i = 0; i < len; i++)
		if ((fld.value.charAt(i) != '0') && (fld.value.charAt(i) != decSep)) 
 		break;
 		aux = '';
 		for(; i < len; i++)
		if (strCheck.indexOf(fld.value.charAt(i))!=-1) aux += fld.value.charAt(i);
		aux += key;
		len = aux.length;
		if (len == 0) fld.value = '';
		if (len == 1) fld.value = '0'+ decSep + '0' + aux;
		if (len == 2) fld.value = '0'+ decSep + aux;
		if (len > 2) {
			aux2 = '';
 			for (j = 0, i = len - 3; i >= 0; i--) {
				if (j == 3) {
					aux2 += milSep;
					j = 0;
				}
				aux2 += aux.charAt(i);
 				j++;
			}
			fld.value = '';
			len2 = aux2.length;
			for (i = len2 - 1; i >= 0; i--)
			fld.value += aux2.charAt(i);
			fld.value += decSep + aux.substr(len - 2, len);
		}
		return false;
}


Then use in the form field:
onkeypress="return(FormataReais(this,'.',',',event))"