Two Select Boxes - Getting Both Values With One Onchange/submit

I have two basic select lists and I want to automatically submit the values from the first list once they select from the second list using onchange. how to get the multiple values from the first select.

So basically I want them to select a state or states from the first list and in the second list they can choose from some data parameters to query within those zip codes. So once they select data parameter(s)... the onchange should kick in and pass both the zip code selections and data parameters to the getData function.

Trying something like:

PHP Code:

<select name="state" multiple size="5" >
<? while($row=mysql_fetch_array($result)) { ?>
<option value="<?=urlencode($row[0])?>"><?=$row[0]?></option>
<? } ?>

[Code].....

By using state.value I get ONE of the select items and not multiple. And I've tried state[] and variations of state[].value or state.value[]... no luck.

The onchange=getData is a function that puts together a URL to get data from another page. So I really need to pass something like state[]=1&state[]=2

Therefore it seems like the state select needs it's own onchange to run a local function that formats this URL string??? then how do I get that value?

I have it working as two completely seperate form elements but I really want to make these two selects one form/step that they have to complete.