This will do it for you.
header("location: http://www.aabbcc.com/" . $_POST['num']);
<form action="redirectform.php" method="post">
<option value="11">Go to 11</option>
<option value="22">Go to 22</option>
<option value="33">Go to 33</option>
<option value="44">Go to 44</option>
<input type="submit" value="GO!" />
On the page we create a select list called num with each number we want in the option values.
In the PHP which handles the submitted form, we check if a value for num was submitted, and if so add a HTTP header with the chosen number. So if we chose 22 the header would look like
This HTTP header is the way to put redirects in using php, so the browser will pick that up and redirect them to the fabulous aabbcc.com.
We also use exit; to stop the php script, as we don't need to process any other code or output the html.
You would probably want to add some things like checking if the value submitted is valid, but that's another topic.
Hope this helps