how to select customer group on registration in magento

 <group_id><create>1</create></group_id> code into the customer account fieldset.

(app\code\core\Mage\Customer\etc\config.xml)
Before adding code:

<fieldsets>
<customer_account>
<prefix><create>1</create><update>1</update><name>1</name></prefix>
<firstname><create>1</create><update>1</update><name>1</name></firstname>
<middlename><create>1</create><update>1</update><name>1</name></middlename>
<lastname><create>1</create><update>1</update><name>1</name></lastname>
<suffix><create>1</create><update>1</update><name>1</name></suffix>
<email><create>1</create><update>1</update></email>
<password><create>1</create></password>
<confirmation><create>1</create></confirmation>
<dob><create>1</create><update>1</update></dob>
<taxvat><create>1</create><update>1</update></taxvat>
<group_id><create>1</create></group_id>
</customer_account>
</fieldsets>

Open the file template/customer/form/register.phtml and add the code  in the form

__('Group') ?>*

__('Group') ?>" class="validate-group required-entry input-text" />
getGroups()->toOptionArray(); ?>

">




save value datbase 

after this line $this->_successProcessRegistration($customer); 
    $customer->setGroupId($this->getRequest()->getPost('group_id'));