Not only is it a different frame size, it's also a different frame rate (30fps compared to the 25fps of the PAL cams). If I were you I'd convert the footage to PAL first.
Puremotion do a "cheap" PAL/NTSC convertor for £109 (I say cheap as you should see how much these things go up to!). Alternatively you could do it the poor mans way and import the footage into VirtualDub, then export as DV AVI (PAL) using frame rate reduction and resize filters.
Not ideal, but I've a feeling Premiere won't let you mix PAL and NTSC in one project.
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