Question: Install 14.04 through live usb to external-hdd on ASUS 105E-DS02, currently running 12.04 with broken wifi. The 8GB live usb and 3 dvds from PRIZX will provide the software. Have read through many answers and web sites, did note the need for internet connection which is not available until thats fixed. Hoping that wifi Atheros ath9k, internal, external Ralink and external rt2800usb Realtek rtl8192 are included in the software. The wifi issue is a seperate question (awaiting answers). Either way I wish to fix 12.04 and install 14.04 on external-hdd. The external-hdd is recognised in 12.04 , and there appears to the ability to boot external drive (recognised WD passport (750 GB) as such in BIOS) and to boot bootable (live) usb (also in BIOS) Any additional help will be much appreciated. Sure miss my now gone linux/bsd library and four servers.

Answer: 
Overall just start the installation but when it gets to the page where it asks you to select install location and such select "something else" then set the bootloader install location to the external hdd and the / mount point on it as well.
You should be able to do this quite easily using manual partitioning. See [this answer](https://askubuntu.com/a/343352/205638) and make sure you're installing to your external, which will likely be `/dev/sdb` and not internal, which will likely be `/dev/sda`. You also have to choose your external for Bootloader Installation as in [this guide](http://www.linuxbsdos.com/2013/10/23/how-to-install-ubuntu-13-10-on-an-external-hard-drive/). You'll most likely have to boot using your BIOS boot menu to choose USB device, since your grub installation on your internal hard drive won't know about the external and vice versa.