a)
many dvd players play both standards - a conversion is allways a loss of quality, the "hardware conversion" of a dvd player is best. so, no need for ntsc>>pal
b)
give ffmpeg a try, it is a mighty tool, search the forums/net for details
keep in mind: different frames per second, different color scheme, different lines per frame...- a professional conversion machine is expensive, i do kmow why
