Why mac pro dual-core Intel xeon 2.66 ghz system 10.5.6 memory 6 gb atyradeonx1900 with boot boot camp when i use window xp pack 3 still can't play call on duty 5?

You have not given us any error messages or what happens when you attempt to run the game. Without any other information, my guess would be that you have not installed the drivers for your video card correctly.