Giusto per info, si può fare il tutto in puro CSS senza javascript. Esempio (il look fa schifo):

codice:
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Esempio</title>
<style type="text/css">
fieldset.choose-form ul, input[type="radio"].form-connect, input[type="radio"].form-connect ~ div {
    display: none;
}

fieldset.choose-form:hover > ul, input[type="radio"].form-connect:checked + div {
    display: block;
}

fieldset.choose-form {
    display: inline-block;
    position: relative;
    vertical-align: middle;
    overflow: visible;
    padding: 0;
    margin: 0;
    border: none;
}

fieldset.choose-form legend {
    display: block;
    border: 1px #666666 solid;
    background-color: #ccaaee;
    padding: 2px;
}

fieldset.choose-form ul {
    position: absolute;
    height: auto;
    /* vertical-menus width */
    width: 160px;
    border: 1px #666666 solid;
    background-color: #dddddd;
    list-style-type: none;
    margin: 0;
    padding: 0;
}

fieldset.choose-form li {
    position: relative;
    float: none;
    display: block;
    height: 28px;
    width: 100%;
    border: none;
}

fieldset.choose-form label {
    display: block;
    height: 100%;
    width: 96%;
    padding: 0 0 0 4%;
    line-height: 28px;
    background-color: transparent;
    border: none;
    color: #000000;
    font-family: georgia, serif;
    font-size: 11px;
    font-style: normal;
    cursor: pointer;
}

fieldset.choose-form li:hover label {
    background-color: #cccccc;
    color: #ff0000;
}
</style>
</head>

<body>

<div>
    Tipo di form: 
    <fieldset class="choose-form">
        <legend>- scegli chi -</legend>
        <ul>
            <li><label for="form-conn-1">Mario</label></li>
            <li><label for="form-conn-2">Enzo</label></li>
            <li><label for="form-conn-3">Dina</label></li>
            <li><label for="form-conn-4">Franco</label></li>
        </ul>
    </fieldset>
</div>

<input class="form-connect" type="radio" name="prima" value="div1" checked id="form-conn-1" />
<div class="form-container">default</div>

<input class="form-connect" type="radio" name="prima" value="div2" id="form-conn-2" />
<div class="form-container">Un form</div>

<input class="form-connect" type="radio" name="prima" value="div3" id="form-conn-3" />
<div class="form-container">Un altro form</div>

<input class="form-connect" type="radio" name="prima" value="div4" id="form-conn-4" />
<div class="form-container">Un altro form ancora</div>

</body>
</html>