Any twitter boostrap(ish) theme for Drupal 6?
Either you may start creating your own theme (you can use any light weight theme as base theme) from scratch using Twitter Bootstrap, or you may check the couple of options present on the sandbox project, which contains experimental code for developer use, as below:


HTML5 CSS3 base Drupal 6 theme built using Twitter Bootstrap: https://drupal.org/sandbox/drewkennelly/1276010 (Also check issue queue of it: https://drupal.org/node/1276060)
A Drupal 6 Theme with Bootstrap installed: https://github.com/sdmunoz/Drupal-6-Theme-Bootstrap
Twitter bootstrap theme for Drupal 6 created using zen as base theme: http://www.eliotdill.com/2012/06/twitter-bootstrap-theme-for-drupal-6/


If any of the above suits your requirement, then you can use them and modify it as per your need, instead of creating it from the scratch.