But is Celeron 420 1.6GHz enough for all processes like for example playing dvd or blue ray movies?
DVD will be easy to play. My 600 MHz Celeron could do it so I'd think a 1.6 GHz Celeron should be just fine for DVD. Blu Ray will probably need more power, I think C2D e6400 is the minimum for that kind of stuff. If you had a video card that decoded Blu Ray like a 8 series nVidia or 2000 series ATi card then the Celeron could probably do it.