The new Screen Sharing functionality in Leopard is not available in the Application folder -- you either need to start it via the Finder or iChat, you can't start the application directly. If you'd like to start it directly, the trick is that once you get it open and it shows up in your Dock, you can right-click on the icon in the Dock and select the "Keep in Dock" option. That way, you can start the screen sharing any time you want.

One problem with this though is that when you start it this way, the first thing you need to do is enter the *exact* name of the computer who's screen you want to see. This is a pain. If you want, there is a trick you can do so that the Screen Sharing application will show a list of computers that are available on your network. To get the list, open a Terminal window, enter the following text into it and then press the Enter key:

defaults write com.apple.ScreenSharing ShowBonjourBrowser_Debug 1

Once you do this, close the Screen Sharing application if it is open. Now, next time you start the Screen Sharing application, you will be presented with a list of other computers available on your network.