In addition to setting up your own private label network, you can buy and sell inventory on their exchange. This lets you appear bigger than you are. For example, if you are able to sign up a publisher in your niche, you can immediately start trafficking relevant ads to show him you're capable. You'll make more money attracting Advertisers in your niche to buy those impressions, but that's a chicken/egg problem that being part of an exchange helps with.
Keep in mind that the entire display ecosystem is already on / moving towards an exchange-based model (rather than a network based model). Most networks now buy a lot of their inventory directly from the exchange.
So if you're looking to start your own network, you should be thinking about building it on top of the exchanges, and you should also have some unique offering: expertise in display / optimization, unique data set, etc.
It sounds like the poster has a niche market he (or she) understands. In that situation, I don't think technology needs to be a selling point.
The hosted version (called OnRamp) would be the place to start - it's free, performs better (it's not all PHP), and gives you easy market integration (which the original comment was referring to). OpenX may or may not be what you're looking for, but at least you can test the waters without any initial investment other than creating an account and setting up a few tags.
(Disclaimer: I work for OpenX.)