but the method im using now is simply to use tmpgenc to slow down the movie frpm 25p to 23,97p (mark "do not frame convert"). Then use besweet to change the audio from 25fps to 23,97 fps
Agreed. Don't try to take 25P to 60i, take it down to 24P (which, as MovieSwede says, is actually 23.976). Encode your DVD at the 23.976 frame rate, and the DVD player will take care of converting it to 60i for you.
well as im understand when you code the menu and so on, its dependent on the orginal mpg. The new one will have different speed so a lot of the settings cant work with the old like chapters. The best thing is to just make a new menu. You have the orginal menu files left?
About quality. It will not look exactly the same. But it will look as close as it will get when you make a 23,976 NTSC version. And it will look better than playing PAL on an NTSC-tv.