You really dont need to defrag a drive with OSX installed.
It seems abit overboard with the information you have gotten, however if it helps you can use the restores disks that come with the MacPro to erase & install the current blank install thats already on there.
or just grab a new harddrive (like the 640AAKS from western digital) for a boot drive. and another for XP.
If you install XP on your machine or even vista, some tools that would be handy are:
AusLogics DiskDefrag (Free Defragging utility for Windows, doesnt run in the background and you manually adjust it, no background processes or anything, probably the best Defragger ive used)
AVGFree (best free antivirus)
HDTach
HDTune
two great harddrive monitoring and benchmarking utilities, analyzes the health of your drives over time.
CCleaner cleans up all the registry and misc garbage.
all of these btw are free and efficient.
As for OSX, the best optimizing you can do is create a Main admin account and then a standard user account you use so if something goes awry you can just recreate the account.
I dont use any OS cleaners for OSX (people recommend Onyx and stuff) but i hardly ever use it. i manually just clear out the clutter of my disk space and caches anyway. and it all runs smooth and fast.
goodluck
