How would I start an advertising service?

Ive found a few good open source adserver programs and I am thinking about starting a business in the field. I was wondering if anyone has any tips and whatnot about how to start getting publishers and advertisers, or any other helpful information that would hopefully guide me on a good path to success.
Im not sure if adserver is the correct term for what I am talking about..but just incase its not, I mean I want to start an advertising website like bidvertiser [dot] com or reachads [dot] com

All info is greatly appreciated! Thanks!!!

Original post by Arson