Sounds like a a good idea(similar to myspace's myAds), but wondering how you go about managing your inventory when more than 1 advertiser has same targetted audience.I really doubt if there's a software that can be worked in this way

However, here's my sugesstion

(1)You may try open source ad servers like OpenX & Google Ad Manager, see if you can create various logins with varied previelige.Or if you can afford you may think of going for a commercial ad servers like zedo, adtech, etc.This way you set different access to different advertisers.

(2)All ad servers including Open source gives APIs.If you a programmer or have programming team, create front end applications what your advertiser would use, and in the backend interface your application with the ad servers API.

(3)In the market there are many small ad server provider, check with them if they can customize their tool as per your requirement.

Hope this helps

Raja Ramachandran

http://interactiveadops.com