Remote Desktop or KVM????

It depends on what your priorities are.

If you're trying to save desktop real estate then you could use a KVM to switch between the PowerMac and the iMac screens (using the iMac's video mirroring to display its screen on an external monitor).

This would work well if you use both machines equally, but only one at a time.

On the other hand, if you use one machine more than the other you might find ARD an acceptable solution to control the other machine periodically. I wouldn't recommend this for 'normal' system usage, though, especially for anything detail-oriented or that is video-intensive (video, games, etc., etc.)

If you need to see both machines at the same time, though, then there isn't really a good option other than to have two keyboards, mice, etc. or use a KVM and just ignore the video option.

If you can deal with two monitors, try Synergy - http://synergy2.sourceforge.net/.

Basically it allows you to use a single mouse and keyboard on two (or more) computers. It uses a "server" and a "client" component. Of course, the computers must be networked so the server and client can communicate the mouse and keyboard movement.

I used this solution for two Windows boxes but have not used it for a good 6+ months.

I'd use VNC (OSXvnc and Chicken of the VNC) before ARD. ARD uses an uncompressed version of VNC, making even 100Mbps seem slow.