This module doesn't work with the 6.x drupal due to API changes in hook_form_alter, and module .info file checking when installing the module. Two fixes:

to autocalc_shipping.info, append:
core = 6.x
php = 5.0

and to autocalc_shipping.module, change line 3 from:
function autocalc_shipping_form_alter($form_id,&$form){

to:
function autocalc_shipping_form_alter(&$form,$form_state,$form_id){

and you should be good to go.