If you can boot into OS 9, you can use DiskWarrior or Norton Utilities (latest versions, of course) to defragment an OS X drive. Just make sure that your file system is NOT journaled, since I don't know of any utilities that'll defrag a journaled drive yet, and they'll screw it up big time if the drive IS journaled and you try to defragment or optimize the drive.
There is some question as to how much benefit defragging has on an OS X drive, or if there is even a benefit at all, since OS X moves files around like crazy, and I've heard that UNIX has an "auto-defrag" of sorts of its own... it's doesn't really defrag, but it moves the files and the bits of files in the order that it likes the most. So even if you defrag, you'll see that OS X quickly "frags" it up again.