Showing your ad units inside the forum is probably the best way to go.
tarunkumar wrote
I would like to display one ad after each thread in post.
You can only display three ad units per page. So maybe you should do what Nabble does: display ads after the first and last posts. Is this reasonable? If yes, I will help you with this setup. Basically we will have to override the "show_custom_ads" macro in your forum. Please post the ads code in your reply.