If you have a version prior to 1.5, you will need to do the following:

1 - Run this mysql command:

INSERT INTO configuration (configuration_id, configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added, use_function)
 VALUES (NULL,'Enable Article Manager Topics Map', 'GOOGLE_XML_SITEMAP_CREATE_TOPICS', 'false', 'Set to true if you would like a site map created for your Article Manager topics (Article manager must be installed to use this option).<br>(true=on false=off)', '289', '12', 'tep_cfg_select_option(array(\'true\', \'false\'), ', now(), NULL);

2 - Upload the following files:

googlesitemap/index.php
googlesitemap/sitemap.class.php
googlesitemap/sitemap.class_Alternate.php
sitemaptopics.xml