How do I ensure that my machine does not have a software key logger ? I.e. that a software key logger isn't already on my machine ?
Like others have stated, you can never be absolutely sure you're not infected, unless you're using cold storage and the container has a physical lock and is under constant trusted surveillance, even then it's not truly secure.
In the meantime, I'd recommend using an offline password manager such as
http://keepass.info/.