Hey rowhan
I've customized my template using the CSS files found within the template (using FTP).
If you use Google Chrome, you can right click any part of a web page and click 'Inspect Element'
When it pops up on the bottom, you can see the CSS rules attached to that <div id> or <div class>.
It can be difficult to get used to at first, but once you get the hang of it there's no limit to how much you can customize a template.
Here's a work in progress - http://dirtprincess.com
Hope this helps a little bit with the 2nd link you put up.