Hi tomatzio,
I looked through your game above. Well done for beating the computer again!
I began to prepare move-by-move commentary of the above game, but after a while my post became unnecessarily long and complicated, so I just wanted to say the following.
I think your main target for improvement ought to be tactics. There were a few tactical shots missed (by both sides!), and I would highly recommend mastering basic tactics first and foremost.
I have not read Chess Tactics for Champions, but I guess that would be suitable, as long as it's not too advanced. If it is a little advanced, Winning Chess Tactics by Seirawan is good. I would also recommend
Chess Tempo.
[Edit: Actually, even Winning Chess Tactics isn't so elementary. Maybe someone else has a better book suggestion.]