Re: Your system is too SLOW to play this!
the Geforce G210 (GT218 chip) is a very low end chip.
Trying to push mp4 decoding and up-scaling at 1080p (be it 50 or 60 Hz) is really borderline for the chip.
Try for a lower resolution first (I mean, you are comparing your intel @ 1MP to the nvidia @2MP).
Also, check in mplayer if you have any image quality options (post processing) and disable most of those, as the chip just cannot perform them.
As the universe is curved, there cannot be a straight answer...