Hook location question

[asandhanam]

I need to display some banners in certain forums & the threads in each of those forums. I have a plugin set up that would grab the correct banner from the database based on the forum id. So i pass $foruminfo[forumid] to the plugin to select the right banner. What should the hook location be? I tried 'forumdisplay_start'. But that works only on the forum pages not in the threads of those forums. Can someone tell me which hook location would work for this situation?