UltimateDefrag Freeware Edition - Free software downloads and reviews - CNET Download.com
If your looking for a free defragger this for me is probably the best on our there.
I've installed this several pc's and have found it very effective.
It's best to schedule it to run so you never have to remember to do it. I would recommend scheduling it to do fragmented files only at login at the very least and depending on your usuage set it up to run do another fragmented files only another couple of times. For the PC's I use during the day it's scheduled to run at login, 10:30 and 14:30, plus it will run after the PC has been idle for 20 mins.
For me the above keeps fragmentation to a minimum and the program quickly defrags the files.
I have also scheduled the auto option to run once a week which does a more comprehensive defrag, if your PC doesn't see much action this can safely be done monthly.
Remember to schedule a task in XP, Vista you need of have passwork on your user account and you need admin rights. I would advice creating another user account to run the tasks from otherwise you will see the program appearing everytime it runs.
If you use it on Vista you will need to run the program as administrator.
The home of Spybot-S&D! See the spybot link for instructions on how to do this.
For me this is the best freeware defragger.
Other free defragmentors to consider.
Defraggler - Defragment your files!
Auslogics - Speed Up Computer and Internet
JkDefrag v3.35