Il codice seguente mostra come l'ho svolta io l'esercitazione. Vedi se ti può essere utile! 
File Form.htm
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Form di registrazione</title>
<link rel="stylesheet" type="text/css" href="stile.css" />
</head>
<body>
<form id = "form1" action=".." method = "post">
<fieldset id = "frame1" class = "down">
<legend>Form di registrazione</legend><br />
<label class = "testo" id = "label1" for = "input1">Nome</label>
<input class = "text" type = "text" id = "input1" tabindex = "1"/><br />
<label class = "testo" id = "label2" for = "input2">Cognome</label>
<input class = "text" type = "text" id = "input2" tabindex = "2"/><br />
<label class = "testo" id = "label3" for = "input3">Corso di Studi</label>
<input class = "text" type = "text" id = "input3" tabindex = "3"/><br />
<label class = "testo" id = "label4" for = "input4">Numero di Matricola</label>
<input class = "text" type = "text" id = "input4" maxlength = "7" tabindex = "4"/><br />
<label class = "testo" id = "label5" for = "input5">Password</label>
<input class = "text" type = "password" id = "input5" tabindex = "5"/><br />
<label class = "testo" id = "label6" for = "input6">Ridigita la Password</label>
<input class = "text" type = "password" id = "input6" tabindex = "6"/><br />
<label id = "label7" for = "option1">Maschio</label>
<input class = "opt" id = "option1" type = "radio" name = "option" tabindex = "7" />
<label id = "label8" for = "option2">Femmina</label>
<input class = "opt" id = "option2" type = "radio" name = "option" tabindex = "8" /><br /><br />
<label id = "label9" for = "textarea1">Varie</label><br />
<textarea id = "textarea1" tabindex = "9" rows = "6" cols = "36"></textarea><br />
</fieldset>
<fieldset id = "frame2">
<legend>Conferma ed invio dati</legend>
<br />
<input class = "cmd1" type = "button" id = "cmd1" value = "Invia" title="Clicca" tabindex = "10" />
<input class = "cmd2" type = "reset" id = "cmd2" value = "Cancella" tabindex = "11" />
<br /><br />
</fieldset>
</form>
</body>
</html>
File stile.css
fieldset {width: 500px; margin-left: auto; margin-right: auto}
fieldset.down {width: 500px; margin-left: auto; margin-right: auto; margin-top: 30px; min-height: 500px}
legend {color: red}
label {margin-left: 10px; margin-top: 10px; margin-top: 10px}
label.testo {display: block; float: left; margin-left: 10px; width: 150px; margin-top: 5px; vertical-align: middle}
textarea {margin-left: 10px}
input.text {width: 150px; margin-top: 10px; margin-left: 5px; vertical-align: middle;}
input.opt {margin-top: 10px; margin-left: 5px}
input.cmd1 {width: 100px; margin-left: 5px}
input.cmd2 {width: 100px; margin-left: 70px}
