forum with pop adverts (help)

I came across a websites http://www.realestniggas.com and i noticed something about the forum , when you click on a particular thread an advert pops up at the back of the page you are viewing . I never knew this could be done for a forum . I would like to know how this is possible as i have always planned of creating a forum with the same pop advert idea.

See original post by muchochiz