I've been playing this with Crossover games for the past 2 weeks. It runs, albeit with a slower FPS than it should considering my machine and the graphical quality. Besides that, it's really immersive and fun. Nothing like wandering through abandoned wilderness in the dark, almost getting mauled by a group of mutated dogs, then sitting down with some other stalkers near a campfire, listening to the sounds of one strum his guitar. For only $20 it's a pretty good value. I should mention that my copy didn't install on Leopard, but after I installed Snow Leopard it worked.
It is awesome, don't know if you'll be able to install mods for it or not, but try the Oblivion Lost mod, adds a lot to it, and it becomes a whole new game. If you like that, try the newer one STALKER Clear Sky. Finished that a couple of weeks ago, another amazing game. And coming soon is STALKER Call of Pripyat <3