Without tax for me also.
Actually with the ability for the admin to award points that your putting in, you could do that using the built in referal tracker that comes with zen cart. Yes it would be manual, but he is probably looking for automation. Just wanted to point out it could be done manually simply by checking the referal report and awarding points manually based on that report. Just have to run it once a day.
Unless you get 100's of new customers a day, manually works. I do it that way now. Read this for how it works
http://pinetreecandles.com/shop/discount_coupon.html. Of course once I can manually award points I will do that.
I wish i knew more about coding so I could help out.

Your doing a great job Andy.