To find the desired partition in GRUB, go to the GRUB command-line (press 'c'), and type:

    find (hd0,0)/   (press 'tab')

This shows you the files on that partition's root directory.  (you can do the same for subdirs)


Or, to identify partitions based on (hopefully) unique files:

    - 8gb thumb drive         find /autorun.bat