Ok, well is there a way to go back to 10.5.4? I am also about to roll back my iPhone as well. It seems that all of those problems that people were having with 2.0.x I now have with 2.1.
Unfortunately, there is no painless way to downgrade OS versions.
The procedure is:
1) Backup all your user data (and anything you need - whole drive is best)
1.2) download the combo updater for version you wish
2) use your Mac installer DVD to boot up the Mac and install the original OS, if you use Archive-and-install, it tries to save most of your existing user settings
2.2) run repair disk from menu/diskutility prior to actual install
3) install the available OS updates to the level you desire (prior to the problematic one) use the combo updater mentioned to dl above.
4) make sure all your data is still there, or use your backup to replace anything missing.
5) for safety, remember to: only have keyboard and mouse plugged in during the install and update, run permissions repair after each major OS update (ie: after initial OSX install, after combo update), run disk repair from the dvd before you start this whole process, don't run any user apps while install or OS update is running, and after the system does its own automatic last reboot, do one more reboot where you reset PRAM by holding down Cmd-Opt-P-R till you hear three startup chimes, then release and should be good at last version.
Check your data and off you go... (this point would be good time to make a CCC clone backup for saving)
Yes, its a lot of work.
And, having said all that, i have done lots of system refreshes for self and others over the years. It happens. Best of luck and wishes.