It used to be that to have remote control ability on Mac OS X it took third party applications. In Tiger they introduced a built in VNC server which is convenient. Now in Leopard, arthritis they include a built in VNC client called “Screen Sharing.”
This is actually the application that is used for “Back To My Mac” or to “Share Screen” with local machines on your network. But, it can also be used as a VNC client to any machine. It’s probably most convenient if you take the app and put it in your Dock. It’s located in /System/Library/CoreServices/Screen Sharing.
There are also other ways to open the app on demand.
In Safari, you can type “vnc://ip_address” in the URL bar, replacing “ip_address” with the actual address of the remote Mac.
In Finder, you can “Connect To Server” (Commank+K) and type it there as well.
Doing either of these things will open the application, begin the connection, and return asking for your login.
(Of course, to have any of this to work, you’ll need to be sure to have either “Screen Sharing” or “Remote Management” activated in your System Preferences -> Sharing panel.)