Ordered the 23" display with the idea of a different Mac later. I actually have the X800 card. I have the 243T back on the DVI and a 172N on the AGP port. The 243T is just unstable and periodically blacks out (then recovers).

SmartGart is set OFF.
The Display Tab doesn't really have much to it... just lists the displays.
Under Options the following are checked:
Re-activate all warning messages
Enable ATI taskbar icon application
Show ATI icon on taskbar
Reduce DVI frequency on high-resolution displays (I've tried this both ways)
Alternate DVI operational mode (i've tried it both ways)

Unchecked is Disable quick resolution feature.

It looks good when it's running but occasionally blacks out for a few seconds and then recovers.

I read somewhere that some cables are not that great. Could this be the problem?