Boot disk on USB memory stick

["Chiu, PCM (Peter) " <P C M Chiu rl ac uk>]

Having looked at some of the discussions circulating before,
I tried the recipe that Bruce Bryne suggested but have hit a "missing
operating system" problem.

Below are the steps I took:

a. mkdosfs /dev/sdc1
b. mount /dev/sdc1 /mnt/stick
c. cp rhas3u2/isolinux/* /mnt/stick
   where rhas3u2 is the RHES AS 3 update2 CD mount point
d. cp /mnt/stick/isolinux.cfg /mnt/stick/syslinux.cfg
e. cp /rhas3u2/images/pxeboot/initrd.img /mnt/stick/
f. umount /mnt/stick
g. echo "mtools_skip_check=1" >> /root/.mtoolsrc
h. syslinux /dev/sdc1

When I took this memory stick to another PC, I can see
the hard disk device (OTi6828) at the BIOS level - Boot option.

But after selected this as the boot device, save and reboot, the system
reports:
PXE-E61: media Test failure check cable
PXE-M0F: Exiting Intel Boot Agent
missing operating system

If I then reboot, the system hangs at the initial memory test. 
After reinserting the memory stick, the system resumes the memory tests, 
but later reports missing operating system error again.

It seems that USB booting is not always possible.

Does anyone know what is it required in order to support USB memory stick
booting?

Thanks.