Wow. Thanks to Philinux in this thread, I didn't realize that the pre-hardy gui configuration tool for graphics cards and screen resolution is still available - it is just hidden in Gnome now. With the new xorg server I suppose this utility is definitely deprecated, but I was surprised to see it.
Basically, you go into System > Preferences > Main Menu, and in the left-hand pane highlight "Other". To the right, enable "Screens and Graphics". Now under your Applications menu, "Other" will show up and you can now fire up the old-style of video / screen configuration gui.
*** WARNING ***: I have only enabled this, but not fully tested it on my G5 iMac. I have no idea about how the integration works with the newer style of screen configurations is (System > Prefs > Screen Resolution). If you do play with this, backup your existing xorg.conf !
One thing that is VERY interesting is if you look under the Apple display menus, you can see a nice wide range of horizontal and vertical sync settings for various popular PPC models. So even if this utility doesn't work, you have a nice reference for what values to use for a manual edit of xorg.conf if it comes to that. Most of the values seem to agree with the various threads and wikis.
Again, I have not tried this on my Hardy PPC box, only enabled it to look around. YMMV!