I've been using US system versions and have no difficulties using PAL with my iMovie or DV system here in Europe. You should open the iMovie preference file in the preference folder (just double-click it and use simple-text to open it), as it's not a regular preference file but a text file. Early on in the file you will see NTSC, change it to PAL, close the file and save when prompted. This might work.
(Thanks to Gretar)