I have this installed on my store as well as Discount Coupon Codes (by KGT Contribution 4269)
I have just also installed CSS Buttons (Contribution 3328) and cannot get the Redeem Button to show on the "One Page Checkout" page.
I think that the line that needs changing is the following, but what do I change it to - any ideas?
<td class="main">' . tep_image_submit('button_redeem.gif', IMAGE_REDEEM_VOUCHER, 'id="voucherRedeem"') . '</td>