The forces of light and dark are constantly at war even a fair-weather movie fan can tell you that. But if you view that eternal cosmic chiaroscuro from, say, Moscow, it'd look something like Night Watch (a.k.a. Nochnoi Dozor). Director Timur Bekmambetov (working from the sci-fi novels of coscripter Sergei Lukyanenko) was more interested in shades of gray: Two contingents, supernaturally endowed ''Others,'' police each other in a sort of ethereal Cold War, and both are morally ambiguous. ''To me, Moscow isn't light or dark,'' says Bekmambetov, who's at work on the second film in his trilogy. ''It's striped like a sailor's vest, and leaves the choice up to you.''