Twice now I have had problems formatting a new Western Digital My Book external drive under 10.5.x. Disk Utility fails to format the drive as Max OS X Extended Journaled with a "Format failed..." message. The first time this happened, I found an obscure firmware update at Western Digital's forums. This time, I found a quicker solution in this thread over at macForums. Here's a short executive summary version:
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080909200624739