sql error during install

Your install functon is missing a single quote around the module name:

function jgrowl_install() {
  // Always keep jgrowl last so we can grab all the messages.
  $weight = db_result(db_query("SELECT weight FROM {system} ORDER BY weight DESC LIMIT 1"));
  db_query("UPDATE {system} SET weight = %d WHERE name = 'jgrowl", $weight + 100);
}

Fixed using:
db_query("UPDATE {system} SET weight = %d WHERE name = 'jgrowl'", $weight + 100);