Cyber Source Payment Method Plug-in For Magento

For Community and Enterprise Editions:

http://www.magentocommerce.com/magento-connect/cybersource-extension.html

Setting Up Instructions:
http://www.magentocommerce.com/knowledge-base/entry/payment-methods-cybersource 

Instructions for Magento GO Edition:

http://go.magento.com/support/kb/entry/name/payment-methods-cybersource/

Payment Method Error Codes:
http://support.cybersource.com/cybskb/index?page=content&id=C156&actp=LIST  

Test Account for Cyber Source:
https://apps.cybersource.com/cgi-bin/register/reg_form.pl