I added an extra customer attribute using this code:

startSetup();

$setup = new Mage_Eav_Model_Entity_Setup('core_setup');

$entityTypeId     = $setup->getEntityTypeId('customer');
$attributeSetId   = $setup->getDefaultAttributeSetId($entityTypeId);
$attributeGroupId = $setup->getDefaultAttributeGroupId($entityTypeId, $attributeSetId);

$installer->addAttribute("customer", "province",  array(
    "type"     => "varchar",
    "backend"  => "",
    "label"    => "province",
    "input"    => "multiselect",
    "source"   => 'eav/entity_attribute_source_table',
    "visible"  => true,
    "required" => false,
    "default" => "",
    "frontend" => "",
    "unique"     => false,
    "note"       => "province",
    'option' =>
        array (
            'values' =>
                array (
                    0 => 'Rome',
                    1 => 'Milan',
                    2 => 'Florence',
                    3 => 'Naples',
                ),
        ),

));

$attribute   = Mage::getSingleton("eav/config")->getAttribute("customer", "province");


$setup->addAttributeToGroup(
    $entityTypeId,
    $attributeSetId,
    $attributeGroupId,
    'province',
    '999'  //sort_order
);

$used_in_forms=array();

$used_in_forms[]="adminhtml_customer";
$used_in_forms[]="checkout_register";
$used_in_forms[]="customer_account_create";
$used_in_forms[]="customer_account_edit";
$used_in_forms[]="adminhtml_checkout";
$attribute->setData("used_in_forms", $used_in_forms)
    ->setData("is_used_for_customer_segment", true)
    ->setData("is_system", 0)
    ->setData("is_user_defined", 1)
    ->setData("is_visible", 1)
    ->setData("sort_order", 100)
;
$attribute->save();



$installer->endSetup();

It works fine in the backend. How to show it in customer frontend dashboard? thanks