Hi, Mitzi.
If you're using the FAT file system, there's no reason for you to bother with anything but the standard (included) defragger in Win2K. If, however, you use NTFS that can be a very different matter. The inbuilt defragger in Win2K doesn't defrag the metadata / MFT. Some (most?) third party defraggers defrag some or even all of the metadata and MFT and pagefiles and registry hives at boot time. Some of them (like O&O Defrag) can do this very quickly and efficiently every time the system is restarted. You have to tell the commercial version of Diskeeper each time you wish to perform a boot-time defrag. Be careful to stay away from any defragger that tries to defrag the metadata and MFT while running in the GUI mode of the OS. That's a certain invitation to disaster. I know that Norton's Speed Disk used to do this, but I believe they may have removed that option in recent versions.
Whether you actually NEED a third party defragger, even with NTFS, depends upon a lot of factors. If you install and uninstall apps frequently, if you move a lot of files on and off of the hard drive(s), if you run apps that really thrash the drives a lot (video editing, big-time databases, etc.), if you've got small file allocation units for some reason (like having converted from FAT32 to NTFS), then a third party defragger can make a big difference in performance. If you don't do any of those things, then the standard included defragger may well be all that you need.
I tend to use Executive Software's Diskeeper on servers because it has a feature called FragGuard that helps prevent internal and external fragmentation of pagefiles and the Master File Table. I tend to use O&O Defrag on notebooks because they get restarted frequently anyway (We move around from site to site a lot.) so O&O's always-on boot-time defragger does the job for us in that respect. And, after you've run it once so that it can assess your system for "unmovable files" you can add those unmovable files to the boot-time defrag routine. One other defragger I've heard good things about is Raxco's Perfect Disk. I tried it briefly several months ago and was put off by some bugs in the interface. But those may well have been fixed by now, and several people whose judgment I trust say it's very good.
Anyway, these all have trial versions, so I don't think it should hurt to try them out. Do be sure to read the installation options carefully. If the option is offered, I recommend telling the installer to back up the original defragger files so that they can be restored if / when you uninstall the third party defragger.
I hope this helps.
Regards,
Jim