Works great on my test install, I am wondering tho should there be a first post restricion at all as a page full of say swf's added with the media tag is going take quite some time to load. I just added 3 in firefox and as they are cached each time no real problem but then I opened the same page in IE which of course wasnt cached and it took some loading time to completely load the page.
I think it should be conditionaled to certain forum ids so it cannot be used where its not wanted and restriced to first post of the thread. Im sure this can be covered with an if /if around the template edit.