Modded to be slightly more useful as I wrote the other one while slightly delirious.
upgrade to latest D6 drush arb default --destination="wherever/you/like" mysql update systemsetstatus='0' where filename like 'sites%' delete 6.x, retain /files and /sites directories, remember any mods to .htaccess drop in 7.0 files drush updb if no error, press y if error occurs, make a note of what you need to do to fix it. If this is a repeat run, fix all errors noted rename/move your Drupal directory (or delete it but in the event you need it later) from above where the Drupal directory should be, drush arr [backup-filename-without-square-brackets].