I'm with Göran, don't try to include PAL footage in your NTSC FCP project .. despite the much heralded ability to mix PAL and NTSC rates in FCP 6, its actually pretty terrible (native conversion of NTSC footage in a PAL timeline is awful anyway).
Far better is to convert your footage to match your timeline
before you start to edit.
Compressor's Advanced Format Conversion capabilities are very good and produce excellent results although the conversion is a very slow process.
Nattress's Standards Conversion plugins are notably faster than Compressor and do an arguably better job of the conversion.
I've never used DVFilm's Atlantis software personally but its certainly got to be far superior to FCP's built in conversion!