Remove Discount Coupon field from view - but retain function

Hi......
I'm attempting to use the Discount Coupon function to track orders placed by Sales Reps on my site. I have had a change made to the ot_coupon.php file to pre-populate the coupon field at checkout with an identifier for the Sales Rep.
I want the full Coupon functionality to remain in the code, but I want to completely remove the Discount coupon field from view on the Payment Information Page.
I suspect it can be done with CSS - but I'm not sure where to start.
Any suggestions?
Also, if I set the Coupon value to $0.01, a record is kept of those coupon transactions in admin. If I set the value to $0.00, the coupon functionality is retained, but no record is kept. Is there a simple change in code that will allow me to track zero value coupon transactions?
Thanks

Try this:

In your admin, go to configuration, define page status, then input 3 (Link OFF/Text OFF) under Define Discount Coupon.

This removes the Discount Coupon from the main page sidebox.

Thanks Decostyle.... but I'm not using the Discount Coupon in the Sidebox.
I have the Discount Coupon field pre-populated with an identifier for Sales Reps placing an order. I would like to retain the functionality of the Discount Coupon, but I want the process to take place in the 'background' - I just want to hide reference to the Discount Coupon in the center column during the checkout process.
So, on the 'Step 2 of 3 - Payment Information' page I want to hide the whole 'Discount Coupon' Box from visibility. In the best of all worlds, I would also like to have the 'Discount Coupon' line in the 'Your Total' Box also be invisible.
.......and is there a change I can make in the code to retain data for a report if I set the value of the Discount Coupon at $0.00?

I was having the very same dilemma and found a solution :)

To only show the coupon code field for specific customers:

1. Give them a specific link that contains a promotion variable

ex. http://yoursite.com/index.php?promo=1234

2. Set a session variable in the header template

**
3.On the checkout page where your coupon code would typically show, hide the coupon code form if the promo session variable is not set - do something like this:**

Hi, this bit of code seem just what I need, but I can't figure out which file to put it and where in the file. Could you help?