ideas for Affiliate Program.....

Hello all, I am working on an Affiliate Program and need ideas or suggestions... please email me if you have any suggestion.... for now my program will keep track of an affiliate_id and the client_ip address for future reward... (i.e if the client buys anything, the affiliate_id gets a credit...) but this system won't reward an affiliate if for example, many clients use the same computer (same ip address) to buy products... then the affiliate_id is only credited once.... Have anyone ever done anything similar and have other suggestions? I am working on it, but is still looking for better ways of doing it... thanks in advance.. KD