Building a affiliate advertising system

I need a affilite advertising system for my website so I can track leads I make for my clients. Its an site jobsite. I know there are existing systems on the market so it should not be that hard to build. I want the system to interfere as little as possible with my clients system. So I am not interested in any complicated systems that requires me to contact my clients programmers everytime I need the affilate system integrated with their systems.