yeah, FCP is no good for standards conversion.
export as a QuickTIme movie,
then run that thru compressor
i guess you can go direct to an NTSC format Mpeg file,
but go into the settings and turn all the "frame control" and "re-size" settings to best.
another thing to consider is do you really have to make a PAL DVD?
99.95% of all PAL DVD players and TVs will play NTSC DVD's, too.
cheers,
nick