The best way to do it is to make a 24fps master from the PAL 25fps source. The PAL source is usually the original 24fps program anyway, just running at 25fps, so its not exactly hard to do.
The other problem with NTSC though is its lower resolution and crappy colour rendition, so you will then have to either resize your master down to NTSC rez, or crop it and lose some of the frame. Either way you are losing some information through interpolation or cutting it off.

Of course if you use a home theatre PC, you can avoid all of these problems and run the PAL master at frame tripled 72fps and get a correct speed, full resolution flicker free luvverly image