Here are some more tutorials about coupons:
http://www.webassist.com/tutorials/eCart-Coupon-series
http://www.webassist.com/tutorials/Static-eCart-coupon-code-II
http://www.webassist.com/tutorials/Static-eCart-coupon-link
http://www.webassist.com/tutorials/Static-eCart-coupon-code-I