To only approve users, you need to combine a multiplexer with the approve workflow: http://ez.no/doc/ez_publish/technical_manual/3_8/reference/workflow_events/multiplexer
You also need to set up the cronjob to run the workflow processing.
This is done by running something like:
php runcronjobs.php from the root of the ezpublish installation.
Setting it up using crontab is described here: http://ez.no/products/ez_publish/documentation/installation/the_cronjob_script
