A USB stick which can be booted to, which has ubuntu desktop on it
Use 2 USB's, one as the installer, and one as the OS.
1) Create an Ubuntu Boot USB the normal way (I used lubuntu 12.10 x64)
2) Unplug all the HDD's from your PC (for safe-keeping)
3) Plug in the boot usb, start up, enter live environment.
4) plug in the dev env usb
5) run the installer (from the desktop of the live env)
6) it will ask if you want to unmount the drive first -- click yes
7) just choose 'install normally'
8) follow the installer normally
9) once it's installed, remove the boot usb, leave the dev usb in, reboot
10) it should boot to your new portable dev env!
making copies of the bootable usb
http://ubuntuforums.org/showthread.php?t=1043014
Find mount name: open 'disks' will be listed as something like: /dev/sdg1 if you click to the other partitions on the drive, you'll see they're all sdg1, 2, 3, etc. the drive name is /dev/sdg
to clone:
sudo dd if=/dev/sdg of=lubuntu-dev.iso
this took me 6 minutes for a 16gb drive
to put onto new usb (warning! purges destination drive, don't put in the wrong drive name!!!):
sudo dd if=lubuntu-dev.iso of=/dev/sdg
this took me 33 minutes for a 16gb drive