This fan-produced film did the rounds ages ago. In fact it was back in 2003 (5 years ago!) when I first heard about it – from this thread at TTLG forums, as it happens.
And, you know what? It’s still as gloriously campy and fun as it was back in the day, as well as being a shining example of what insane fanboys with a budget can actually produce when they put their minds to it… Batman vs. Alien vs. Predator – no one expected that! Talk about a mashup…
Just imagine how the audience would react if Christopher Nolan pulled that kind of stunt in his upcoming The Dark Knight. Although it would of course be unforgivable (and would no doubt result in a sustained hate campaign from legions of die-hard fans), it would almost be worth it simply because of the supreme “WTF!?!” factor and stratospheric levels of internet kudos which such a move would generate.