Booting ubuntu from usb hdd: GRUB menu not shown

"Assuming you have the valid menu.list, I think the commands you want are:

root (hdX,Y)
setup (hdX)

where hdX is probably hd0 or hd1 and Y is the partition number, starting from 0.
Note that grub numbers primary partitions (0,1,2,3) and logical partitions (4,5,6,7).

The 'root' command will check for the right partition type.
The 'setup' command will check for the right files in /grub or /boot/grub (on that partition).

For example, if your internal hd contains non-linux windoz stuff and the first partition on your USB drive is /boot, then try:

root (hd0,0)

and if that works:

setup (hd0)

OR

root (hd1,0)

and if that works:

setup (hd1)

Then reboot and select the USB drive at the bios boot menu."