I keep having to re-install Ubuntu after trying advice. This is very frustrating. All I want is to boot to a Linux command prompt. Please help!
You're probably best off with the Ubuntu Server install. By default it installs only the basic system, resulting in a fast machine with a small memory and disk footprint. http://www.ubuntu.com/download/server/download
Use the Ubuntu minimal CD to install a base system.
It will contain the Linux kernel, basic Linux tools and the Debian APT system to install any other packages you might need manually.
The downloaded ISO for 11.10 is 23MB and after install (on my system) occupied around 600MB (rest of packages to install the system are downloaded via a network connection).
You will be able to choose the packages you want during the installation or after your reboot your system you can install anything individually with
apt-get or by choosing packages by typing
It might be easiest to do all your command line stuff from a LiveCD such as the one you used to install Ubuntu? If you have access to Windows and a flash drive you can always try UNetBootin to make a LiveUSB.