Just had exactly the same issue arise and discussed with various people. Seems that it is just possible that a PAL DVD might play in the USA. However I have opted for making an NTSC version of my DVD as follows:
I opened a new project, selecting NTSC format. Next I copied as menu assets all the original menus from the PAL project. I then used Canopus Procoder to convert all my PAL avi to NTSC versions (including the avis used in the motion menus).
I reopened the PAL project and noted down the time for each chapter point in the timeline, and the name I’d given it. Next, opening the NTSC timeline I added chapter points – it is esay in the project window to type in the required timecode to shift each chapter point to its correct location.
Finally I linked each menu button as before.
If it sounds a little time-consuming and a pain, it was! However the NTSC DVD plays fine.