@ madis71

Some sites have reported that there is a problem with the Dos7 (Win) Format bootsector image for floppy drives. There is a partition sector type in the bootsector, it is 1 for fat12, 6 for fat16 and eh to 11h for Win95 fat16,fat32, lba and extended.
if you can load your USB key with the diskette image on it, and plug it into Linux
find out what linux calls your USB key, for example /dev/sda
run fdisk /dev/sda
Enter
1 (for 1 partition)
6 (for fat16 this is recommended, though you can try 1 for fat12)
p to display
w to write the modified flag

I know nothing, I tried it , it didn't work but I still think it's the right thing to do.

@ordata51
There is a big difference between a floppy and harddisk bootsector. The harddisk boot sector includes the harddrive table which contains pointers to the rest of the MBR structure which will spread over 3 or more sectors, this happened when DOS 5 or 6 allowed a directory within a directory. A floppy bootsector has no harddisk table so stays in the 512byte limit of one sector. The CHS characteristics handle the 360, 720, 1.2, 1.4 floppy but can go to max for "superfloppy" devices.
By the way, I'm a Linux newbie and just installed Suse Linux and couldn't see my USB key. Well my luck, SUSE Linux 9 has problems with USB and also doesn't have a hexeditor.
http://www.4p8.com/eric.brasseur/suse9.1_usb_stick.html