Normally, under OS 9 and OS X, a G4/400 cannot handle hard drives that exceed 128GB in size. People tell us that's because of the IDE/ATA hardware. So tell me why ... booting from an OS X 10.1.5 partition, my Samsung 160GB hard drive can be formatted up to 149 GB (1K = 1024 Bytes), and partitioned as I liked. And it can then be used under OS X 10.3.3 with full capacity.
Only drawback: OS X 10.3 cannot be installed on the last partition, otherwise 20GB will be lost. But even under OS X 10.3.3, this last partition can be used for storage etc. So if you have a large hard drive, an older Mac, and the 10.1.5 version of OS X, try formatting the drive there; you may be surprised by the results.
[robg adds: I can't confirm this one as I don't have access to an older Mac with which to test. However, if true, I know a few people who would be quite happy. If someone else tests this, please post your comments.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2004041920292676