Magento: how to change “Search entire store here”

edit the file
/app/design/frontend/yourthemepackage/yourtheme/template/catalogsearch/form.mini.phtml
example
/app/design/frontend/default/default/template/catalogsearch/form.mini.phtml

and change the code below

var searchForm = new Varien.searchForm('search_mini_form', 'search', '<?php echo $this->__('Search entire store here...') ?>');