Xbox that cant be chipped ?

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Hi all. Admittedly this is not my field @ all (Xbox). Ask most things about PC's and ill know what were talking about. Anyway onto my problem. I bought a X-box (for one of my son's) about 3 years ago (2002). It was chipped in 02 and play's all backed up games.

Now i recently bought my younger son an X-box also for christmas.(it was bought 1/2/05) I took it to a guy who chipped the other X-box and left it with him for a couple of hours. When we went to collect it i was told that this perticular type of X-box can not be chipped as of yet ?. So is it true that the new modle X-box cant be chipped ? Or is it a case of him not having the right mod chip for the new X-box ?. I ask because i was under the impression "ALL" X-box's could be chipped to play backed up games. If the new X-box (ones for sale in UK shops) can not be chipped then any idea as to how long were talking here ?

All info will be greatly appreciated by myself and more importantly my 10 year old son. He hates not being able to play the "backed up" games his older brother plays on his chipped Xbox. Thanks