Just keep in mind that you should never do anything else with the computer while your defragging. I tried running all sorts of processes while defragging with Diskeeper just to see if it was true and I managed to increase the level of fragmentation by almost 5000% (yes five thousand!). It took the entire night to get it back to normal
Just let it run once befor shutting down the computer and it shouldn't take too long, depending on the size of your disc of course.
And also: Defragmenting the swap-file and the registry is important, but the defragger that comes with Windows95 doesnt do that (unless you do some complicated shit to get around it) so buy a proper one!