I can't get defrag to run

I have had problems trying to defrag C: drive and have found a site that was
a help,

http://www.winhelponline.com/article...indows-XP.html.
I was getting messages defrag not installed on your computer and I used this
and got back disk defrag but it still will not work can any one help me?
I have windows XP pro with sp3

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mml