JkDefrag is a free disk defragment and optimize utility for Windows, various version, it will also work with Windows Vista. The software works much faster than the defrag utility that comes with Windows and can be interupted at any time during the process. The software will also defrag floppies and USB sticks. The latest version includes the windows version, a command line version, a version that works as a screen saver (e.g. kicks in when your not doing anything on the computer) and a DLL library that can be used with programming languages.
Being true opensource the source code is available online to download if required. To install the software just unZip the files and run the .exe. There are plenty of command line options to tell the software what to leave (do not defrag). Remember to delete all the rubbish from your hard disk before running as you do not want to waste valueable time defragging stuff that is only going to be deleted at some stage. The wonderful ccleaner utility (again free) will do this for you in no time and is very comprehensive often gaining 100’s of Mb’s of disk space in a few seconds.