One Site. Multiple Demos. Serving Relevant Ads, How?

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I have a wiki-like site. I reckon I have hundreds of different demographics visiting the site.

1. How do I work out the demos for the visitors of each page?
2. And then using a script (OpenX? Or what?) how do I then only show specific adds to the relevant demo?
3. And can I then have those demo ads follow them around the website as they browse?
4. Would using Facebooks Open Graph/Connect/??? API help me in serving ads to my visitor?

Confused :ugone2far:

 

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Help me out guys.

In return, I give you the scoop on Grunin's dark side:

UPDATE: Powell jury recommends death sentence - Georgetown, DE - Sussex Countian