Extended File Allocation Table (exFAT), first introduced with Windows Vista SP1 is a file system designed especially for flash drives. Advantages of exFAT in comparison to FAT32 are the removal of the 4 GB file size limit and support for storage devices with large capacities. A major advantage of exFAT is that it's a file system that's both readable and writable on Mac OS X Snow Leopard (starting from 10.6.5) and Mac OS X Lion (Windows' NTFS is only readable on OS X, not writable).
Although not supported in the default installation of Windows XP, you can install this update from Microsoft (KB955704) to bring exFAT file system support parity to XP.
Check this article to know how to re-format a flash drive to exFAT.