Well...first off this is not something I've had to do myself, and secondly I'm not sure theres an easy way to do it.
What I would try would be use dvd decrypter to extract the movie from the .iso, and set it not to split the files so I got one big .vob. Then I'd try to convert it with WinAVI from dvd to dvd format, changing the settings to output NTSC and set it to fit on a dvd. WinAVI might also work if you batch convert the .VOB's and choose to "merge to one".
It's also possible that WinAVI would read and convert from the extracted VIDEO_TS folder directly, but again, never tried it. You could extract the VIDEO_TS with Isobuster if Decrypter wont do it, and if you need to join the .vob file, use Dvd Decrypter to extract from the VIDEO_TS set not to split the files.
That's just the first thing I would try personaly, and I don't know what the results would be. Some combination like that should work, but you will loose your menus and stuff.
Hopefully someone else will be able to give you a tried and tested method that will also preserve your menus and so on. If such a method exists (and really you'd think it would!) Best of luck. I'd have a look around google if I were you using terms like PAL dvd to NTSC and other such variations, see what comes up.
Looks like patching the headers does not work for your player anyway, so a full conversion is the only way. Personaly I'd buy a new multi-region player with MPEG4 capabilities as well, as you can get them starting around Â£26 GBP!
EDIT: Do your burned disks from the iso play ok on your pc? Might be best to try to rip the vobs or from the dvd, or use it as a convert source for whatever conversion program you choose to use. Some prefer reading from the disk, some prefer the folders on you hard-drive first.