Drupal 6 - Theme custom search form results
Whatever u have done so far is correct. Only thing left now is to render the content from ur preprocess 'rootcandy_preprocess_rootcandy_my_search_results' to ur 'rootcandy-my-search-results.tpl.php'. U have to start debugging in this way.


Check ur $vars['form'] contains ur form values in  'rootcandy_preprocess_rootcandy_my_search_results'
create a variable in preprocess and try using it in ur rootcandy-my-search-results.tpl.php.
Eg: $vars['testing'] = "this is to confirm that variable is working in rootcandy-my-search-results.tpl.php"
if you print $testing in ur rootcandy-my-search-results.tpl.php and it gives "this is to confirm that variable is working in rootcandy-my-search-results.tpl.php" Which means its working fine.
Then you can pass ur form results to the tpl file. 
Eg: $vars['result'] = drupal_render($vars['form']['result']);


Try this. Ur first goal will be making sure u can get ur preprocess values in ur tpl file.