I Need To Choose A Password For My Computer Login, How Do I Choose One That Is Unbreakable?

That's impossible, some piece of computer coded software could eventually, given enough time, find your password if allowed.  Experts at IBM and other firms can usually get most people's passwords within ten guesses (or at least what it might be).

From my experience, you password should not be:

Your name
Your address
Your previous address
Your school
Your current or ex-girlfirned
Your favourite word
Your favourite foreign word (they have dictionaries!)
Your home town
Your pets name
Your favourite band or its album or song.
Your favourite movie or an actors name

If you are going to create a strong password, you are actually going to have to choose something that is both difficult to guess and difficult to remember.  A random combination of letters and numbers is the only way to ensure a very safe password, no one could guess and even a computer would take a long time trying to try all the combinations of letters and numbers possible.