Unable to Create Bootable USB Disk - Need Help

[David Hunt]

I know I must be missing something easy. I really hope someone can help 
me. I have a LexarMedia 128MB USB JumpDrive. I managed previously, 
through lots of effort which I obviously can't duplicate, to create a 
bootable drive using mkbootdisk in Mandrake 9.2. Using this, I installed 
FC1.

I am trying to find and understand a generic way of:

1. Partitioning the USB key
2. Creating the filesystem.
3. Copying the diskboot.img files
4. Booting linux from the usb drive

So far I have tried the following:

sfdisk /dev/sda

    /dev/sda1 : ,,b,*
    /dev/sda2 :
    /dev/sda3 :
    /dev/sda4 :
    y
sfdisk -l /dev/sda

    Device   Boot   Start   End   #cyls   #blocks       Id   System
    /dev/sda1   *      0+      983   984-   125951+   b   Win95 FAT32   
    /dev/sda2           0        -         0         0              0   
Empty
    /dev/sda2           0        -         0         0              0   
Empty   
    /dev/sda2           0        -         0         0              0   
Empty

dd if=/dev/zero of=/dev/sda1 bs=512 count=1
mkfs.vfat /dev/sda1
mount /iso/FC2/FC2-i386-disk1.iso /mnt/cdrom/ -o loop
mount /mnt/cdrom/images/diskboot.img /mnt/floppy/ -o loop
(at this point usb drive is already mounted at /mnt/removable)
cp /mnt/floppy/* /mnt/removable

Pressed F12 on startup to get boot menu
Selected USB drive
Displayed message is "This disk is not bootable..."

I can open the usb drive in Windows or Linux and read the contents. It 
all looks OK, but obviously this isn't working.
Anyone know why?