The "?" basicallly tells the preprocessor (ASP in this case, or php if used there) that variables exist. Then depending on the code on the resulting page, you would need to script the page accordingly to pull those variables for use.
The real problem is that you can't use php to first verify the value, and act accordingly since the php is processed before the output is sent to the browser.
What you need to do is either write javascript that would direct you to a certain page based on the value, or...
On the resulting page (would be the same page whether cobor was yes or no), call the variable, and include an appropriate file, or code.
Example:
On your form page:
<FORM method="GET" action="nextpage.php">
<INPUT type=checkbox name="cobor" value="yes" checked>
</FORM>
On your resulting page (nextpage.php), you would do something like:
// Get the variable from the URL
extract($_GET);
// Verify the value, and act accordingly
If (isset($cobor)):
switch ($cobor):
case "yes":
include('cobor_yes.inc');
break;
default:
include('cobor_no.inc');
Endswitch;
Else:
include('cobor_no.inc');
Endif;
Obviously, you would need to taylor the code to your needs, but this should get you started with figuring out where to go... (or at the least, get you confused enough to ask more questions 😉)