Add the second sidebar to theme ?

Possible? Totally.

Piece of cake? Not really. All depends on your HTML/CSS skills.

Well, you could go to websites that have tutorials on three-column design and what the CSS needs to look like.

However, after reviewing your website (which took too long to load… I have a cable connection and it almost took me 7 or 8 seconds… ) I would say that you would be better off reading some material on web design THEORY and the principles of good web presentation.