Add more field in admin configuration in magento
devm.com.np
// system.xml
<address translate="label,comment">
    <label>Address</label>
    <frontend_model>module/adminhtml_addmore</frontend_model>
    <backend_model>adminhtml/system_config_backend_serialized_array</backend_model>
    <sort_order>32</sort_order>
    <show_in_default>1</show_in_default>
    <show_in_website>0</show_in_website>
    <show_in_store>0</show_in_store>                        
</address>

<?php
//block
class Company_Module_Block_Adminhtml_Addmore extends Mage_Adminhtml_Block_System_Config_Form_Field_Array_Abstract
{
     
/**
     * Prepare to render
     */
    
protected function _prepareToRender()
    {
        
$this->addColumn('country', array(
            
'label' => Mage::helper('module')->__('Country'),
            
'style' => 'width:50px',
            
'renderer'  => Mage::getModel('adminhtml/system_config_source_country')
        ));
        
        
$this->addColumn('address', array(
            
'label' => Mage::helper('module')->__('Address'),
            
'style' => 'width:100px',         
        ));
      
        
        
$this->_addAfter false;
        
$this->_addButtonLabel Mage::helper('module')->__('Add More');
    }
    
    protected function 
_renderCellTemplate($columnName)
    {
        if (empty(
$this->_columns[$columnName])) {
            throw new 
Exception('Wrong column name specified.');
        }
        
$column     $this->_columns[$columnName];
        
$inputName  $this->getElement()->getName() . '[#{_id}][' $columnName ']';
        
$value         $this->getElement()->getValue();
                
        if(
$columnName == 'country')
        {
            
$rendered '<select name="'.$inputName.'">';
            
            
$options Mage::getResourceModel('directory/country_collection')->loadData()->toOptionArray(false);
            
            foreach(
$options as $option)
            {
                
$rendered .= '<option value="'.$option['value'].'">'.$option['label'].'</option>';
            }
            
            
$rendered .= '</select>';
             
            return 
$rendered;
        }
        else
            return 
parent::_renderCellTemplate($columnName);
       
 
       
    }
}
?>