The default theme of Drupal is okay. Garland is much better than the earlier Drupal default theme but it has some, uh, issues. The typical way to develop a new theme is to start from one of the contributed themes and hack it up. ATCK offers a different route in terms of building a theme from scratch.
Instead of hacking up an existing theme ATCK has you use a WYSIWYG Grid Builder service which spits out HTML to implement the chosen grid. That's your starting point.
However I don't like this support and have deinstalled ATCK.





