try perfectdisk ive gone from perfectdisk 8 to perfectdisk 10 which im using now on xp pro, been using it for over a yr and it works great, some defrag programes can cause certain things to slow down but with this everything is fine game loading times opening aps, as for how much it will improve speed of pc comes down to how much u have on and how long has it been b4 ur last defrag, also perfectdisk has a smart placemant option that seems work well, i only use that when ive installed new things
I use Diskeeper Pro. Excellent utility that auto defrags in the background whenever necessary without manual intervention. Defrags system files, page file, multiple drives simultaneously etc. Also has a file placement algorithm that sorts/sequences files based on the frequency of usage.
Auslogics Disk Defrag for me. Free, pretty quick and is all you could ever really need from a defragger. Nothing to stop you using Windows' tool if you wanted to.
To keep defragging time to a minimum, try running it daily. It is far easier to let your PC defrag for a maximum of 5minutes every night than it is to wait for it for an hour every month.