Weekly Famitsu has revealed that
Namco X Capcom is in the works at Monolith Studios, the guys behind the wildly popular
Xenosaga line of games. It sounds like a fighter (and honestly, it really should be) but it's actually an RPG that will combine the most beloved characters from both companies' stables. It'll be interesting to see how it turns out but honestly, I can't think of one Capcom RPG character that I'd like to see in a crossover game. Square-Enix, perhaps, but not Capcom.
No word on the platform yet but since the game is Japanese, it's safe to say that it'll either appear on the PS2 or the GameCube. The smart money is leaning towards the PS2.