In order to add a new attribute to your magento installation, you can use following method:

Create an instance of Mage_Eav_Model_Entity_Setup class and use its method addAttribute() to add one.

$setup = new Mage_Eav_Model_Entity_Setup(’core_setup’); $setup->addAttribute($entityTypeId, $code, $attr);

$attr is an array containing Attribute elements (like frontend and backend model, default value, etc.)

For details look at the sourcecode:

app/code/core/Mage/Eav/Model/Entity/Setup.php