We've got some proprietary cookie targeting software which we are developing to help deliver better targeted ads. We don't have a group of publishers, nor particularly want to go and build our own network as this is almost as difficult as building the targeting software. Are there any networks out there that will let us run our own cookie targeting script on their network and publishers. 
Ad networks that let you run your own cookie targeting
advertising;cookie;ad targeting
Sam, what you are trying to do is to read third party cookies. I'm afraid, that is something nobody can do, nor are ad networks able to do that.Each domain can only read its own cookies and there is no way to have domain A read cookies set by domain B or domain C.More infomation about how cookies work, the differences between first-party and third-party cookies, their restrictions and what is possible and what isn't, can be found here, here, here (nice illustrations too) and Wikipedia of course.