# fdisk /dev/sdb
d -> delete all partition
n -> create a new primary
t -> type '6' for vfat 16
a -> toggle bootable flag
w -> write and exit

# mkfs.vfat -F 16 /dev/sdb1

# aptitude install syslinux
# dd if=/usr/lib/syslinux/mbr.bin of=/dev/sdb

For AMD64:

# mount /dev/sdb1 /mnt
# mkdir /mnt/syslinux
# cd /mnt/syslinux
# wget http://ftp.de.debian.org/debian/dists/unstable/main/installer-amd64/current/images/hd-media/initrd.gz
# wget http://ftp.de.debian.org/debian/dists/unstable/main/installer-amd64/current/images/hd-media/vmlinuz
# wget http://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-6.0.1a-amd64-netinst.iso

# vim /mnt/usb/syslinux/syslinux.cfg

default vmlinuz
append initrd=initrd.gz ramdisk_size=12000 root=/dev/ram rw

# umount /mnt

# syslinux -d /syslinux /dev/sdb1

That's it :)