Tonyk,
1)You must buy the Microsoft Hi-Def pack, which has to be bought from importers and costs about £40 - DONT buy anything made by anyone else!!!
2)You must get hold of the PAL/NTSC video switcher disk available on the net
3)Change the video on your XBOX to NTSC and then you will have another menu under video options on the MS dashboard. Tick all the Hi-Def options and off you go!