diff -up contact_orig/contact.pages.inc contact_categ/contact.pages.inc
--- contact_orig/contact.pages.inc	2007-10-15 12:42:19.171875000 -0500
+++ contact_categ/contact.pages.inc	2007-10-15 13:56:26.484375000 -0500
@@ -35,6 +35,10 @@ function contact_mail_page() {
       $default_category = $category->cid;
     }
   }
+  drupal_set_message("a:".arg(1));
+  if(arg(1) && in_array(arg(1), $categories)) {
+    $default_category = array_search(arg(1), $categories);
+  }
 
   if (count($categories) > 0) {
     $form['#token'] = $user->uid ? $user->name . $user->mail : '';