function replaceCharacters() {

    var textboxes = document.getElementsByTagName("INPUT");
    var textAreas = document.getElementsByTagName("TEXTAREA");
    var field, str;

    for (var i = 0; i < textboxes.length; i++) {
        field = textboxes[i];

        if (field.getAttribute("type") == "text") {
            str = replaceTxt(field.value);
            field.value = str;
        }
    }

    for (var i = 0; i < textAreas.length; i++) {
        field = textAreas[i];
        str = replaceTxt(field.value);        
        field.value = str;
    }
}

function replaceTxt(txt) {

    var newString = txt.split("<");
    newString = newString.join("(");

    newString = newString.split(">");
    newString = newString.join(")");

    newString = newString.split("\"");
    newString = newString.join("\'");

    return newString;
}