I use the current Diskeeper Home 10 which 2007 replaces. I think its really very good indeed. I have it on "set it and forget it" so it just purrs away in the background without any need for interuption from me.
I particularly like the "boot time " defrag which defrags the system files which cannot be defragged when the system is working.
My only reservation about upgrading now would be that the "read me" file does not mention support for Vista, it may well but some further investigation would be needed. If you do not plan to upgrade to vista it will not matter.