Welcome to the sevenforums! first off. XP will see ready access to the factory Fat volumes generally seen on flash drives and external hard drives due to that version's backward compatibility. With Vista and 7 the first move with any seeing that is to simply go into the Disk Management while the drive is plugged in and right click on the partition to select the reformat option
What that will do is reformat the existing partition to NTFS 5.0 which is native to Vista and 7. You should have ready access to it following that. With data already on however you may be able to see that converted to the NT file system using the method outlined at How to convert a FAT16 volume or a FAT32 volume to an NTFS file system in Windows XP
That can be touch and go at times where the best is to backup anything presently on the two and proceed with a normal reformat. With external drives as well as a larger Kingston 16gb model I boot from a live GParted cd and simply delete one to see another brand new created and formatted simply another way to insure integrity.