[souperman]

What are you trying to do exactly?

You pass the url like this:

$urlcode = "<a href='www.domain.com/file.php?id=".$vbulletin->userinfo['userid']."'>Link</a>";

echo $urlcode;

Then on the external php file:

$userid = $_GET['id'];

//sanitize if used in a query
$userid = mysql_real_escape_string($userid);

Of course thats how you would do it, but you really need to validate the userid because anyone can change the value via url.