to speed up your PC the best is to backup your data, format the system partition, reinstall Windoze and then reinstall the applications you need...
defragmenting your HDD is another good way if it is VERY fragmented. Also installing RAM is quite all right - but beyond 2GB it is worthless for everyday work if you are not editing large pictures or video files.

another good way to speed up your PC is to get a new one

No software in the world can speed up hardware... eventhough those tools sell quite well