To start index your /var/log/secure, and search on it.
source=/var/log/secure login
and look at the format of your events to narrow your search.
You can use the splunk search language to extract the fields you need, probably user and result.
see the field extractions manual or the rex command http://docs.splunk.com/Documentation/Splunk/6.0/SearchReference/Rex
Then count the number or success and failures per user.
<mysearch> | stats count by user result
or a chart
<mysearch> | chart count over result by user
etc ....
for the search commands, look at http://docs.splunk.com/Documentation/Splunk/latest/Search/Whatsinthismanual
