[Simon Lloyd]

You shouldn't need a mod, just make it required always and editable, but you could redirect them on login if the filed is empty. in a plugin with glbal_complete as the hook:

PHP Code:

if (THIS_SCRIPT != 'profile' AND $vbulletin->userinfo['fieldx']==''){
/* Redirect browser */
header("Location: http://www.yourwebsite.com/profile.php?do=editoptions");
exit;
} 


this is redirecting to edit options assuming the profile field is there, replace fieldx for the actual profile field.