Just chasing some help for something.

I've got Gift Cards which are basically plastic cards with a code on the back. Each card has it's own code which have been set up as discount coupons.

I also want to have mass discount coupons which are codes that will go in places like newspapers where people can get 5% off or something like that.

Now, for the people who buy the gift card I want the card to be able to cover postage (not free postage but if they spend $40 and postage is $10 they can use a $50 gift card to pay for the lot) but if they use the code for the 5% discount, I don't want postage to be included in the calculation.

So basically the solution I came up with was to duplicate the ot_coupon module and have one version which includes postage and one which doesn't.
I'm struggling to get it going though and I was wondering if anyone can give me a run down on what changes I need to make to duplicate the module.

thanks.