why would you want to do that? swf/flash is not recommended for anyone to include in a website since it has developed very serious security issues over the last couple of years. many new softwares do not even support it to begin with.
all current browsers support html5. not being a game, I can't say for sure, but I would bet that most of the old flash games are available now in html5.
oh, I assume you are talking about a phpbb bulletin board site. that is what this support board is for. anyway, you can turn on flash in the admin panel and then you can use a flash bbcode to insert a flash file in a post. I don't know if that will do what you want or not.
either way, I would suggest you do NOT do flash at all, but hey, it is your board.
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