function doInputCheck(field,valid) {
    var ok = "yes";
    var temp;
    for (var i=0; i<field.value.length; i++) {
        temp = "" + field.value.substring(i, i+1);
        if (valid.indexOf(temp) == "-1") ok = "no";
        
        if (ok == "no") {
            field.value = field.value.substring(0, i);
        }
    }
}