Without more information, it's difficult to help. In the case of an over the air antenna, you still need an ATSC to NTSC convertor, and then an NTSC to Pal convertor.
If you are talking about a DVD then try importing it into your computer and converting it to an avi file. Then make a DVD from the avi file in PAL format. I have done the reverse. You can usually find freeware to do this.