I believe so. Because on ATi's website it says that such and such motherboard are now comoatible with CrossFire. Although I'm not sure if that's the truth or just another way for ATi to make some extra cash. Either way, I certainly don't have the cash to get one. So as far as testing this theory out, I can not do.
But the cool thing will be to see what this X1900XTX can do. Because they've never released an XTX series card before. So what this new signia has in store is goign to be fairly neat to see, plus what kind of overclocking potential this new card has. If it's anything liek the X1800XT, then I'm sure you can get 1.8+ GHz core clock and possibly, dare I say it, 3+ GHz memory clock?