how to add multiple currency in magento ?

If you think show multiple currency in magento is difficult task. than you're wrong thinking . follow below step and see multiple currency works..

GO to Admin >> System >> Configuration >> Currency Setup (click left tab) and select multiple currency in "Allowed Currencies" using ctrl key and save this setting.

Now Go to  System >> Manage Currency >> Rates and fill custom price on text or if you want market price than click on Import button only and save

how to get store config value in Magento?

<?php echo Mage::getStoreConfig('isis/isis_order_setting/enable_isis'); ?>

In 2 ways you can find the path of store config value .

1) open Database and see the "core_config_data" table and see the "path" column. find you're module here. and use path value.

2)  open System.xml file and find section, groups and fields values.
you can find this file on app/code/<pool>(community,local,core)/Namespace/Model Name/etc/system.xml
 this is my system.xml file path app/code/local/Magentoo/Isis/etc/system.xml

Below is our dummy system.xml file
<config>
   <sections>
      <isis translate="label">
<groups>
            <isis_order_setting translate="label">
  <fields>
                  <enable_isis translate="label comment">
 </enable_isis>
</fields>
           </isis_order_setting>
         </groups>
     </isis>
  </sections>
</config>