passing JS variables to PHP pages

Hi, i have a JS generated drop down box system, is it possible to pass the variables picked by a user to a php page for querying a web site. at the moment i have set the select boxes using:

s1.setAttribute("name","s1");
s1.setAttribute("id","s1");

and i'm trying to call them in the php page using

$var_name=$_POST['s1'];


but it isn't liking it one bit!
I've got a feeling this is a little too simplistic?
Any ideas?
Steve

The user picks them after the php is already done executing and the response has been sent to the client.
You can't get javascript variables into PHP without a second request to pass them, either via a URL querystring, a form submit, or xmlhttprequest (javascript).

If you use the querystring or form with GET method, use $_GET['s1'].
If you use a form with POST, use that $_POST['s1'].

The drop downs aren't populated by any database variables, just plain text i'm using a form submit and POST but with no luck
cheers
steve

How are you submitting the form?
A user action, or javascript?
And what's the error you get? By "not liking it", what do you mean? What are the values you are giving the options in the select?