My notes on how I've constructed CALI's Drupal multi-site setup are on the CALIcon07 wiki. The directions are for building subsites that are off the root of a base Drupal install, community.cali.org/clea. Some folks have pointed out that sites with unique URLs, clea.community.cali.org, may not need the symbolic link highlighted in the article. I haven't investigated this fully yet, but will make any corrections once I do.