If you type 'history' (without the quotes) in your x-term, it'll pop up a list of the last 500 commands you've attempted to execute. Each one is numbered.

Say you scroll back in the list a bit and you see psx4m is number 437, in your x-term simply type:

!437 (and hit enter)

It'll run that command.

You can also create aliases in your shell config file - for bash it's .bashrc (if you are root), for the 'user' account I believe you can use .profile - though don't quote me on that : )