I recently saw this on DVD after years of putting it off. I admit I'm not that big a fan of the Alien films, I find them too slow paced to tell the truth, and the only one I liked was Alien: Earth Hive, and that's a book, not even one of the films (alright, so I did enjoy the Alien 3 Megadrive game also). As for Predator I thought the 2nd film was lame, but did enjoy the first one, and the Batman VS Predator comic book.
Onto Alien VS Predator. I think cross overs are a neat idea in principle, Freddy VS Jason was amazing if simple fun. I thought this film was ok, but not something I would ever watch again. A massive temple buried under ice in the Antarctic is discovered. A team of explorers heads there to investigate, as do a team of Predators. It turns out once every 100 years young Predators head to the temple to do battle and test their Predator-ness. Deep underground a Alien Queen is chained up in a block of ice and unfrozen by the Predators every century to produce Aliens for the Predators to do battle with.