you do realize that even if you managed to get xp to state that dx10 is installed, you will also have to go into your drivers and force it to use dx10 and if memory serves, does xp's drivers even have any dx10 stuff in them? i highly doubt it since there would be no need since dx10 natively does not work on xp and including the dx10 parts in dx9 only drivers would be a waste of space.
please correct me if i am wrong though but seriously, can not enable dx10 in xp if the drivers do not have it as well, its like running .net 3.5 code on a pc with only .net 2.0 installed. though i am not 100% sure on all of this though

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