>the remaining issue is, if I'm in case (1), above, and have redirected to the captcha-containing webform, AND sucessfully submitted the captcha, NOW i want to "continue on" to the search submit, with the originally submitted search parameters.
Have a look at drupal_execute http://api.lullabot.com/drupal_execute not sure if this is what you are trying to do though but pretty sure that if you call this with your submitted values in $form_state['values'] (arg2) and $form_state['rebuild'] = TRUE (arg2) it will do the processing and redirect as per usual (it won't redirect without the rebuild member - have a look at http://api.lullabot.com/drupal_process_form )
