Cart information is not going to CCAvenue

Hi,

I am using 6.x-1.0-alpha1 with Drupal 6.20.
I need to send the "Cart contents" information to CCAvenue in their "Special Instructions" field.
Rest of the fields are integrating well with CCAvanue. e.g. Customer information, Delivery information, Billing information etc.

As I understand that Order Comments goes there in the "Special Instruction" field. How can I just replace this field?

Please help me doing this.