Hi all
Try and get a copy of this defragger called iDefrag from
Coriolis Systems :: Products :: iDefrag, as the UNIX code the runs in the background in OSX does not de fragment your hard drive and disk utility is very limited in what it can do.
I have used this recently on 7 G5s and all machines had severe fragmentation and three of the drive catalogs were damaged!
Disk Warrior will have very little effect!