README.txt

Here's how I edited it.

It should work, but I haven't really ran it through the browser.

Also, if you WANT it to work for IE5, you can include the 'map' function as shown in: 
https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/Map#Compatibility

flip.js

// JavaScript Document
function flip() {
    var b = {
        a: "\u0250",
        b: "q",
        c: "\u0254",
        d: "p",
        e: "\u01dd",
        f: "\u025f",
        g: "b",
        h: "\u0265",
        i: "\u0131",
        j: "\u0638",
        k: "\u029e",
        l: "1",
        m: "\u026f",
        n: "u",
        p: "d",
        q: "b",
        r: "\u0279",
        t: "\u0287",
        u: "n",
        v: "\u028c",
        w: "\u028d",
        y: "\u028e",
        "[": "]",
        "]": "[",
        "(": ")",
        ")": "(",
        "{": "}",
        "}": "{",
        "?": "\u00bf",
        "\u00bf": "?",
        "!": "\u00a1",
        "'": ",",
        ",": "'"
    };
    document.getElementById('flipped').value = document.getElementById('original')
        .value
        .toLowerCase()
        .split('')
        .map(function(a){return b[a] ? b[a] ? a;})
        .join('');
}

page.html

<!--

   This is the only relevant part of the html. It's only a snippet.

-->

<style type="text/css">
form#flipForm { width: 470px; }
#flipForm input, #flipForm textarea { float: left; clear: left; }
#flipForm textarea { width: 468px; height: 100px; }
</style>

<form name="flipForm" id="flipForm">
<textarea rows="5" cols="50" id="original" name="original"></textarea>
<input type="button" value="Flip Text" onClick="flip()">
<textarea rows="5" cols="50" id="flipped" name="flipped"></textarea>
</form>