A few flash elements could really improve the forum, but it should probably be kept small for those who have slow connections.
If a user doesn't have flash installed, they should get that nice little pop-up telling them to install it. They'd be missing out on too many cool things elseware on the web.
I will never look at an eel the same way again after watching "More Eels". If you don't know what I'm referring to, feel blessed you haven't.
Nah...I wouldn't suggest flash, I have seen several forums with flash banne and have always been annoyed with them...for one, the banner takes too long to load on 56k (which i used back then) and second is that not all people have the latest flash player or flash at all....
What you could do is that if someone dosn't have flash it directs them to one page, and if they do it takes them to another. Or they could choose flash or not flash or something like that.
I personally think that a little flash header can be cool, but is often overused.