The movement I was referring to is the subject movement in the video, or the camera movement if you are panning or zooming. When the conversion is done simply by removing frames, there will be little jumps in the motion that are quite noticeable. Even if you use a slow shutter speed, which normally smooths motion by adding motion blur, you will still see the jumps because the frames are removed in post, i.e. after the motion blur is added.
The dedicated hardware/software Dixon mentioned will be able to do frame rate conversion that interpolates or synthesises frames properly and produces smooth results. But for most people this is quite an expensive solution.
Why do you want to convert your footage to PAL anyway? As Dixon mentioned, DVD players and TVs in Singapore can play NTSC footage without converting it to PAL.