Screen sharing is the nifty new craze sweeping the nation - but Leopard users only need apply, right? No! You, too, if you're a Tiger user, can hop on the electric funk train. (Yes, I'm punchy following Leopard's release.) All it requires is a checkbox and maybe an extra piece of free software.

Screen sharing enables remote control of another Mac OS X system running Leopard. You turn the feature on in System Preferences by selecting the Sharing preference pane and checking the Screen Sharing box. (You can choose to limit access to certain users, too.) You can access a remote screen in one of four ways with Leopard - and a fifth trick works for Tiger:

• With iChat, any other iChat user running Leopard can share your screen with your permission (just as though they were initiating video chat), although you can control that behavior, too. Screen sharing via iChat can automatically traverse NAT gateways that handle private addressing for networks created by Wi-Fi and broadband routers; NAT otherwise stymies access from outside the local network.
• With the Screen Sharing program, which you can find hidden in the /System/Library/CoreServices folder (a folder chock-a-block with other nifty doodads, too). Launch Screen Sharing and then enter the IP address or domain name for the computer you want to connect to. With this method, the system you're trying to reach must have a routable IP address.
• On the local network via the new Sharing section on the Finder's sidebar. Select any server in the list, and then click Screen Sharing in the upper right, to the left of Connect As, if file sharing is also enabled on that same server, or by itself if just Screen Sharing is turned on.
• With a .Mac account that you use on multiple computers, the Back to My Mac feature provides access to both network volumes (via File Sharing) and remote control. (Back to My Mac, in turn, is activated in the .Mac preference pane in the Back to My Mac tab.) Back to My Mac, too, can handle NAT traversal.

The fifth approach couples Leopard's Screen Sharing feature with Mac OS X 10.4 Tiger. It turns out that you can make it possible to control a Mac running Tiger remotely from a Leopard-based Mac by turning on the Apple Remote Desktop service in the Sharing preference pane's Services tab on the Tiger Mac. That enables just Tiger-from-Leopard control.

For the Leopard-from-Tiger direction, you need a separate, free application. Screen Sharing is based on, and compatible with, VNC, a widely used remote-control protocol. You can thus use a VNC client under Tiger to connect to Leopard systems. First, on the Leopard Mac, in the Sharing preference pane's Screen Sharing item, click Computer Settings, and then check the VNC box and enter a password; note that VNC doesn't rely on or integrate with Mac OS X user accounts. Back on the Tiger Mac, install the free Chicken of the VNC, and use it to connect to and control the Leopard Mac. (A VNC client on Macs running older versions of Mac OS X or computers running other platforms can also work with Leopard's Screen Sharing.)

Chicken of the VNC can discover local systems, including those running Leopard, that are sharing screens by using Bonjour; or you can enter a remote, routable IP address.

Screen Sharing plus NAT traversal simplifies having remote access to your own system or systems, as well as providing tech support to colleagues and your family members.