Confirm module uninstall
In Drupal 6 you can alter the system modules uninstall form.   

function MYMODULE_form_system_modules_uninstall_alter(&amp;$form, &amp;$form_state) {
  if (isset($form['modules']['MYMODULE'])) {
    //alter form how you would like
  }
}


The only change for Drupal 7 is there is an additional function argument 

6       hook_form_FORM_ID_alter(&amp;$form, &amp;$form_state)
7 – 8   hook_form_FORM_ID_alter(&amp;$form, &amp;$form_state, $form_id)


NOTE: This form gets call on the /admin/module/uninstall &amp; /admin/module/uninstall/confirm.   If you just want it on one then add an additional case to the if statment, checking the path.