It looks like the link that guest has suggested will cost you $20.
It looks like you can download a trial version.

Have you not got the original CD's for windows 98?

If you have, then try the following, although my gut feeling is that you dont need the CD

you need to reinstall the program in windows setup.


Start/settings/Control Panel/Add & Remove/Windows setup


If defrag is not listed as being installed, put check in, apply and
reboot.


If the program is listed, uncheck, apply and reboot. Then go back in
and put check back in and apply/reboot.


Hopefully that works for you. You may not even need your windows CD