There's a somewhat-hidden feature in Mac OS X 10.4 that allows you to rotate any monitor in increments of 90 degrees. If you press the option key while opening System Preferences, and continue to press the option key while selecting the Displays preference panel, you may see an option for "Rotate" on each screen's panel. (I say "may see" because when I tried this on my 800MHz PowerBook G4 it appeared, but when I tried it on my much older 667MHz PowerBook G4 and 500MHz Power Mac G4 it did not. I suspect this is a Quartz Extreme feature, because the Safari RSS screen saver is similarly available only on the newer machine, and I know that's a Quartz Extreme-only screen feature.)

The screen rotate feature could be valuable even if you wanted to use an old CRT monitor in a rotated orientation because it fit your screen layout needs better. You could just lay the monitor on its side and suddenly have a portrait workspace.

Out of caution, I would recommend being prepared for a crash before trying this option. The danger is that not all monitors can handle the frequencies and resolutions associated with the rotated dimensions. What happens if you try it on a monitor that can't handle it? When I tried this out of curiosity on my secondary CRT monitor attached to the PB G4 800 (a pretty good Dell trinitron), the result was several shrunken interlaced images of the screen in rotated form on the CRT. Basically, the monitor couldn't display it correctly. And unfortunately, I couldn't read the screen well enough to find the Rotate popup menu on the now messed-up screen to put it back to normal (unrotated) mode. Nothing I attempted to click on the CRT's display panel would get it back. It behaved as though nothing was clickable.

Unfortunately, the Rotate feature doesn't seem to have the automatic undo that you get when trying a new resolution (the "click OK if this is working" thing, which reverts back to the previous, good mode, if you don't click OK within 15 seconds).

Fortunately, there's another new feature of Mac OS X 10.4 that came to the rescue: another new button on the display panel, called Gather Windows. It's valuable for getting back to a workable state when you have multiple monitors and can't get to one of them. When you click Gather Windows on the display panel that you can see, Mac OS X will move the other monitors' display panels over to that one, so that you can set their resolutions, rotations, frequencies, etc. That is, if you can get to any one of your monitors, you can easily adjust the others' settings.

After a couple of attempts at different resolutions and frequencies, I did eventually get the old Dell CRT monitor to work at 90 degrees rotation.