[cflsystems]

Ok I took it a little bit further because I don't want to force customers to login, register or fillout checkout info just to see how much they can save with the coupon (I know they can do simple math but still...). So I wanted the coupon discount form on cart page and last checkout page.

Thanks to David and Ralph. Here is my customization

1. Open skin1/customer/main/cart.tpl, find

{include file="modules/Discount_Coupons/add_coupon.tpl"}

and change to

{include file="modules/Discount_Coupons/add_coupon.tpl" ch_step="0"}

2. Open skin1/modules/Fast_Lane_Checkout/checkout_step_3.tpl, insert the discount coupon code (you can take it from the file above) and change the line with include file to

{include file="modules/Discount_Coupons/add_coupon.tpl" ch_step="1"}

3. Open modules/Discount_Coupons/discount_coupons.php, find (in 2 places)

func_header_location("cart.php");

and change to

if ($ch_step == 1)
 func_header_location("cart.php?mode=checkout&paymentid=".$cart["paymentid"]."&keep_https=yes");
 else
 func_header_location("cart.php");

4. Open skin1/modules/Discount_Coupons/add_coupon.tpl, find

  <form action="cart.php" name="couponform">
    <input type="hidden" name="mode" value="add_coupon" />

and after it insert

    <input type="hidden" name="ch_step" value="{$ch_step}" />

5. Open skin1/customer/main/cart_total.tpl, find (in 2 places)

<a href="cart.php?mode=unset_coupons" alt="{$lng.lbl_unset_coupon|escape}"><img src="{$ImagesDir}/spacer.gif" alt="{$lng.lbl_unset_coupon|escape}" /></a>

and change to

<a href="cart.php?mode=unset_coupons&ch_step=1" alt="{$lng.lbl_unset_coupon|escape}"><img src="{$ImagesDir}/spacer.gif" alt="{$lng.lbl_unset_coupon|escape}" /></a>

6. Run cleanup.php