Behodar:gehenna: They could just be NTSC which can be region free but won't work in a PAL Xbox.
Region-free NTSC games will work in an unmodified NZ/PAL Xbox; I have a few of them. As far as I know, the only issue with NTSC is with the TV, and I think that's largely irrelevant with HDTV.
Ahh good, I stand corrected. Good to know!