We are thinking of a move to the US in the not too distant future and my DH has alreadyt started thinking practicalities. Will a UK X Box work in the Us or will he need to buy a new one?
I don't think so. The US uses a different TV format than we do. They use NTSC and we use PAL and the US games use a different region code too. You might be able to get your machine chipped to enable it to work over in the US before you go.
Different models of X Box need different things doing to them.
Best to ask at your friendly local independent games store.
My advice would be to sell your uk one and buy another over there. Chipping/modding your 360 will result in you being permanently banned from x-box live, and you would have to import any new games you want from the UK (US games will not work on it).