When you navigate in the Mac Finder, the title of the Finder application shows the name of the current directory. Here's how it looks:

Default Mac Finder Window Title

You can make a quick tweak to your configuration, and have Finder show the complete path in the title of the Finder window. Here's how that looks:

Customized Mac Finder Window Title

If you want to make this customization to your Finder window, it's easy to do. Just open a Terminal window (the Terminal application is in Applications > Utilities) and enter the following line:

defaults write com.apple.finder _FXShowPosixPathInTitle -bool YES

once you hit Enter, you need to restart the Finder application. You can't just close the window, it needs to complete get out of memory. To do that, enter the following in your terminal window:

killall Finder

Once you do that and you start a new Finder window, you'll have the full directory path shown in the title.

Oh yeah, forgot to mention, this only work in Leopard.