php check boxes and url

Sorry - this:
<input type="checkbox" name="custname<?php echo $row_orders['ID']; ?>" id="custname<?php echo $row_orders['ID']; ?>" value="1" <?php if ($_SESSION[base64_encode($row_orders['ID'])] == 1) { ?>checked="checked"<?php } ?>/>

Should be this:
<input type="checkbox" name="custname<?php echo $row_orders['ID']; ?>" id="custname<?php echo $row_orders['ID']; ?>" value="1" />

Please see my edit directly above

Also, how do I usew this to build the url I mentioned ?

I think we need a little more explanation of the part about "build the URL"  What information do you want to put into the GET request?  Where does it come from?

This is the checkbox input:
<input type="checkbox" name="custname<?php echo $row_orders['ID']; ?>" id="custname<?php echo $row_orders['ID']; ?>" value="1" />

This generates the url - I use the "$csv_url2 .= $csv_url2."p=1";" which works fine. What I simply need is to be able to dictate the customer name which is used in the url by the checkbox. ie if the checkbox is checked, that customer name is used in the url. Obviously the first part of the script below is not correct. It would be helpful to me if you can adapt this script rather than using a new one

//generate CSV link url
$custname = "unchecked";

if (isset($_GET['custname'])) {

if ($custname == '1') {
$custname = 'checked';

}

}
$csv_url2 = "p=1&";
do {
if (!empty($_SESSION[base64_encode($row_ordersb[ID])])) {
      $csv_url2 .= "cn[$row_ordersb[CustName]]&";
      }
} while ($row_ordersb = mysql_fetch_assoc($ordersb));
$csv_url2 .= $csv_url2."p=1";

There is not enough of a script there to adapt, and I would only be guessing about where the data comes from and where it goes to.  Can you please post the entire script (please use the code snippet) for both the form and the action script, thanks.

Can you simply give me an example of how to build a url from check box data - if the check box is checked, the data is put into the url, if it is unchecked, it is not put into the url.
The script above is working for me BUT it does not recognise whether the check box is checked or not. I just need to know how to tell the script that the checkbox is either checked or not checked

I didn't manage to get  a working script but did learn some new methods