The problem is converting to NTSC. PAL is a 50-field, 25 FPS while NTSC is 60 field, 30 FPS.
You will need to re-process the video to convert the frame rate. Then, if you're lucky the soundtrack won't de-sync.
Nero recode might work with little hassle, but if it does not, There's a lot of free tools out there to perform this, but none has the simple elegance of Nero recode.
www.doom9.org has articles and links that should get you started. You will learn more than you ever wanted to know about how much of a pain in the ass video really is.