On Wednesday, May 30, 2012 05:52:50 PM you wrote:
> Could someone please provide with a simple and efficient way to install S.L
> from a USB stick?
> 
> I have had so many problems with this, tried so many methods and failed so
> often... I have also wasted so so much time on this... :o(
> Please I need a linux/SL guru to shed some light on this!
> 1) I tried with dd, it alomost never works...
> 2) the livecd-iso-to-disk method works ok but I cannot start my box without
> the usb stick...

Many motherboards will cause an attached USB disk/stick to become /dev/sda as seen by the Linux kernel.  You have to work around this separately when installing, and make sure you remember to install the bootloader to whatever drive actually is the boot drive for the installed system.  The installer gives you options to change the BIOS order of the drives and put the bootloader to any of them.

The CentOS wiki contains most of this information, and most of that is applicable to SL as well as upstream EL.  See in particular:
http://wiki.centos.org/HowTos/InstallFromUSBkey

I have done several USB-key based CentOS installs using information from this wiki article, both CentOS 5 and CentOS 6, and I would expect that ScientificLinux would work the same way.