Adding redirect with coupon code

I want to set up my shopping cart so when a customer enters a coupon code it not only discounts their product but also sends the same coupon code to Share A Sale. Share A Sale is another company we use for marketing. I have spoken Share A Sales tech people and they told me to add this code to Product Carts shopping cart. Here is what they said;

Force a redirect at the time of the coupon code entry
1) You will need to maintain a database that relates a particular coupon code with a ShareASale affiliate ID number
2) When this coupon code is entered in to your site, you will direct the client through a ShareASale redirect link. The link you need to send them to is:

http://www.shareasale.com/r.cfm?b=132163&u=XXXXXXX&m=18169&urllink=&afftrack=

Where you replace the XXXXXXX with the affiliate ID number that the coupon belongs to. You can do this via a hidden iframe or an ajax call, or you could do it inline. If you do it inline, you will need to specify a page that the client should be returned to. This is done using the urllink parameter. If, for example, you wanted to return the customer to the following page:

http://www.wallpaperforwindows.com/store/pc/viewcart.asp

You would code the redirect link like this:

www.wallpaperforwindows.com%2Fstore%2Fpc%2Fviewcart.asp&afftrack=">http://www.shareasale.com/r.cfm?b=132163&u=XXXXXXX&m=18169&urllink=www.wallpaperforwindows.com%2Fstore%2Fpc%2Fviewcart.asp&afftrack=

The http:// has been removed, and the remainder has been URLencoded.

3) You then continue on the checkout process as normal.

I have made a coupon with a coupon code using the same number as a Share A Sale affiliate ID number. This number is 305157.

My question is: Where would I put this code they are talking about? On what file would it go and in what part of the file? I appreciate any help or other suggestions you can give me.