multi select in custom module magento

$tool_cat_Arr = array(array('value' => '1', 'label' => 'Shirt'), array('value' => '2', 'label' => 'Tshirt'), array('value' => '3', 'label' => 'Custom'));


$fieldset->addField("tool_cat", "multiselect", array(
"label" => Mage::helper("storeinfo")->__("Tool Category"),
"name" => "tool_cat",
"values" => $tool_cat_Arr

));