help!!! I dont want to format my USB storage device!!! Erase free space dont function

hi guys: (Macbook pro and Leopard last update)

I have a KINGSTON 1 GB USB storage device!!! It only has 4 files appearing in FINDER (about 1 MB used) but when a look at GET INFO appears: 750 MB used!!!!

I used DISK UTILITY and ERASE FREE SPACE!!! but USB INFO remains the same!!! I need to save a 550 MB FILE!!! But I dont want to ERASE ALL INFORMATION from my USB!!!

How can I erase these "hidden files" wherever they are??? and use that space??? I explored it in QUICK LOOk, looking for HIDDEN FILES !! Appears only Cache, temporary files folder etc....but how can I delete them??? Are they SO BIG FILES (749 MB!!!))

Thanks guys!!!! (MY USB DEVICE HAS FAT32 FORMAT) I need to release free space!!!

When you plug it in, does your trash can show that there is stuff in the trash? That would be my guess. Plug it in and then empty the trash. A similar situation may pertain to Window's version of the trash, since you say it is FAT32. Plug it in and empty the trash on both a PC and a Mac and you will likely get your space back.