I'm going to answer the last two posts separately: Below I've copied the very helpful Samsung notes that John linked to, because it timed out on me a couple of times. I DID manage to get into Ubuntu through my USB drive (yayyyyy!!!) using the first set of instructions, but did not succeed in changing my bios options through the second set of instructions: it only took me to the same blue DOS screen with the items I described above. I'm now going to go try thing the things Phil has suggested and will report back soon (I stopped for a much-needed wine break).

For the benefit of anyone else reading this who might need the info, John's link says the following*. That page also provides a screen shot of where F2 should take you, but in my case didn't - so I still haven't cracked changing the bios options, which means there's no point (yet at least) in installing Ubuntu onto my Drive D. Back soon (and MANY thanks).

*Netbook :
Can I boot my notebook through an external memory card?
You can boot Samsung notebook from a pre-formatted, bootable USB Memory Stick or by changing the boot order in BIOS. Booting from SD card is not supported.

[THIS WILL WORK ON THE SAMSUNG N145 NETBOOK]
        •        To boot from a pre-formatted, bootable USB Memory Stick
        1.        Insert the memory stick into a free USB port and turn on the computer.
        2.        Press and hold F9 at the Samsung splash screen, the computer should now boot from the USB memory stick.
      NOTE: To make a USB key device bootable, you will need to use a third party application.

[THIS WILL NOT WORK ON THE SAMSUNG N145 NETBOOK - TAKES YOU TO A DIFFERENT SCREEN FROM THE ONE ILLUSTRATED]
        •        To boot by changing the boot order in BIOS
        1.        Press F2 at the Samsung splash screen to enter the BIOS setup.
        2.        Navigate to the Boot page.
        3.        Use F5 / F6 to move bootable devices up or down in order of preference.
        4.        Move the USB Key device to the top of the list to boot from it every time it is inserted into a USB slot.