Try to download a diskboot.img, something like :

http://mirror.stanford.edu/yum/pub/centos/5.3/os/x86_64/images/diskboot.img

Then:

fdisk /dev/sdc
mkfs.ext3 /dev/sdc
dd if=diskboot.img of=/dev/sdc

Note:be sure that the usb is unmounted.

dd if=/dev/zero of=/dev/rad3 count=20
dd if=install-media-5.4R3.2-domestic of=/dev/rad3 bs=64k