Speaking as some one whos experienced and has done it before.
Allowing users to post such things (html . swf etc) is kinda dangerous.

Although there is nothing wrong now, some time in the future you'll get a
dick who thinks he's badass. And will be malicious. He'll probably use this to
his advantage...I suggest moderating the post that are in this forum before
allowing them to be posted.

Viral.
The Hallow Life - You'd be amazed sometimes.