My PowerMac G5 tower recently experienced a disaster. I was able to replace the unit with a very similar unit, and moved in my hard drive. It's working great.
I've been using an external hard drive for Time Machine backups.
I decided after moving in to the "new" G5 to hook up my external drive and do another incremental backup.
I received the error messages that are associated with a different motherboard - the backups are associated with the old logic board's MAC address.
Apparently there is a relatively easy way to fix this with Snow Leopard and later - a terminal command called tmutil.
Not so in Leopard.
I found the following thread at Mac OS X Hints, and spent quite some time reading it: http://hints.macworld.com/article.php?story=20080128003716101
I felt somewhat intimidated by all the tinkering with extended attributes, and opted to use a link from the thread which lead me to a script that would automate the process.: http://hints.macworld.com/article.php?story=20081216145458979
I ran the script, it gave no error messages, and reported that the previous backups had been succesfully inherited to the new computer and Time Machine.
I can now run Time Machine, it does incremental backups, and if I boot the computer from my Leopard DVD, I can do a full restore to various points in time.
However, the Time Machine GUI application is "broken". There is no past. The only time available is NOW, even though there have been 2 or 3 recent backups, and many before then. There is no way to roll back in time, choose a file or folder and restore it.
Summary: Time Machine is creating backups, and the Leopard DVD believes it could restore the whole hard drive with them. But the handy user interface is useless - for all users.
I am very close to doing a complete scorched earth reset and simply begin doing Time Machine all over again, just to get the user interface to work.