Two quotes from the EULA on a T23 with IBM XP Preload:
This End-User License Agreement ("EULA") is a legal agreement between you (either an individual or a single legal entity) and the manufacturer ("Manufacturer") of the computer system or computer system component ("HARDWARE") with which you acquired the Microsoft software product(s) identified above ("SOFTWARE").
The term "COMPUTER" as used herein shall mean the HARDWARE, if the HARDWARE is a single computer system, or shall mean the computer system with which the HARDWARE operates, if the HARDWARE is a computer system component.
Together these provisions imply that, for people running the IBM preloaded XP, it's licensed to their "computer" not to a particular hardware component, eg. a motherboard. If MS tried to tell people who replaced components in a "computer" that they need a new license, they would run into problems.
Besides, according to the first sentence in the first quote, the EULA is "a legal agreement" between "you...and the manufacturer" (IBM). As part of the purchase price, "you" got a license from IBM to use whatever OS came with the machine and the license should continue regardless of how many parts are swapped out. Remember, computer and hardware are the same thing "if the hardware is a single computer system"
Which is not to say that tfflivemb2's experience of having to call wouldn't happen. But one should never need to buy a new license for the original OS on the same "computer"