How to remove validation on zip code in magento checkout page?

Login to your your magento admin panel then go to System -> Configuration->General. From Country option tab you can see there is an option "Postal code is optional for the following countries" Select the country which you want to Optional/Not validate . then click on save config to save your settings.



That's it you are done.

How to get the customer login, logout, register and checkout url?

Mage::getUrl('customer/account/login'); //login url 
Mage::getUrl('customer/account/logout'); //logout url
Mage::getUrl('customer/account'); //My Account url
Mage::getUrl('customer/account/create'); // Register url
Mage::getUrl('checkout/cart'); //Checkout url