i installed win 7 on my mac book, and the sound driver was installed successfully, but i don't hear any sound, please help

Do the normal Windows things, start by removing and reinstalling the driver.

Post in the Windows Forums for better help.

Is the volume muted? Click on the volume icon in the system tray to see if it shows as muted. If that's the case, I know of a workaround to fix this because if you unmute the speakers now, the condition will come back when you reboot your computer. I don't know the exact steps off the top of my head at the moment as I'm not in front of my machine. Check this first and reply if muting was the problem and I will detail the steps needed to fix the problem.