Windows XP needs relevant package to support exFAT. Please download the package from the following link.
http://support.microsoft.com/kb/955704/
You can not format StoreJet to exFAT file system under windows XP OS before completing installing the package.
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You can now format StoreJet to exFAT file system.
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Please refer to the following link for more information about common operating systems and their supported file systems.
http://www.transcend-info.com/Support/FAQ-614