How to Integrate 2checkout Payment Gateway

I am new o opencart, i really like the opencart, i hve currently installed opencart v1.2.7 released 5th May, 2009.

i can see 2checkout Payment option in list of Payment Method, & can find these options,

Status:
Geo Zone:
Order Status:
entry_email
Test Mode:
Sort Order:

i don't know in which code, where to provide 2checkout Information so, it can redirect to 2checkout.com for payment processing.

getting error,

Fatal error: Class 'Controllerpaymenttwocheckout' not found in C:\xampp\htdocs\opencart\system\engine\controller.php on line 35