I have customer id .
Using customer id i want customer address.
so how to get customer address and using country id how to get full name of country
Thee address information is stored within the Mage_Customer_Model_Customer so you should be able to create an instance of it with the customer id.
$customer = Mage::getModel('customer/customer')->load($customerId);
Then depending on the type of address that you are looking for you should be able to call one of the following functions.
Primary Billing Address:
Primary Shipping Address:
General Address Selection:
As to the country information, by ID do you mean the ISO standard code for the country eg FR, GB etc in which case you could try:
$countryName = Mage::getModel('directory/country')->load('FR')->getName();
echo $countryName; // Should output France in this example
Magento Customer Model API Documentation: http://docs.magentocommerce.com/Mage_Customer/Mage_Customer_Model_Customer.html