The Samsung varient of the chromebook uses the arm architecture rather than the x86 architecture everyone else uses. The standard ubuntu builds you can download off the ubuntu site is unlikely to be used. There is a port to that system called ChrUbuntu that apparently has partital support at the moment.
Instructions cribbed from the link, with appropriate additional information and warnings posted. I've not tried it myself, so do at your own risk.
Firstly, going into developer mode will wipe anything on the chromebook, unless its backed up to the cloud. You probably don't but its worth noting. You can do so by pressing as per google's instructions - enter recovery mode by you holding down the ESC and Refresh keys and poke the Power button.
Configure wifi but don't log in, and open up a terminal with ctrl + alt + ←
Login as chronos with no password.
wget http://cr-48-ubuntu.googlecode.com/files/arm-chrubuntu-3.sh; sudo bash arm-chrubuntu-3.sh - this runs a script that walks you through partitioning your drive, and installing ubuntu. It will ask you to set a size for ubuntu and reboot. You will have to configure wifi, open the terminal and run the script again. It'll download a bunch of files then reboot into ubuntu.
You can login using the username and password user, then do what you need to do. As it, chromeos will be the default, you can switch to having ubuntu as the default with
sudo cgpt add -i 6 -P 5 -S 1 /dev/mmcblk0 and switch it back with
sudo cgpt add -i 6 -P 0 -S 1 /dev/mmcblk0