On Mac’s snow leopard (or most other OS X versions), the finder menu bar on top of the screen is fixed and can’t be hidden.
This is not a flaw or shortcoming, its been designed that ways because the finder menu bar turns into an open application’s menu bar so in most cases it is required. However, there are some applications like Firefox or Apple Mail where I really don’t need the menu bar. Removing the menu bar in such applications actual gives me valuable screen real estate that I like to use.
I’ve found a cool way to customise applications on the mac so that finder menu bar remains hidden while those applications are being used. It works perfectly, the bar appears when the mouse pointer is moved to the top edge of the screen and hides when the screen is in use.
Here’s a small video of how you can change your apps to do the same , before you try it, I suggest you backup the Info.plist file that is edited in the video
In case the video doesn’t play on your system, you can download it here