hi folks,
I've been using this software at work on servers to keep fragmentation of files to a minimum and it works REALLY well.
It runs in the background and doesn't affect other applications. If you find your PC isn't running as fast as it was when you bought it then a lot of this can be down to fragmentation, Diskeeper replaces the windows defrag tool with a much more powerful one that keeps your hard disks performance running optimally at all times.
I run it on a very busy email server that is constantly reading and writing thousands of small files and it works brilliantly.
Unfortunately it isn't free but then not much that is this good ever is.
www.diskeeper.com