After you have requested a trial version of EventSentry you should have received an email that will show you on how many computers you can install EventSentry. In the email look for the line LICENSES in the trial activation info, which will show you the number of computers you can install the licenses on.
When requesting a trial version, you can choose how many computers you wish to monitor with EventSentry and select the appropriate value from the "Number of Installations" drop-down list.
You can request an extension to your trial license or extend the number of computers of your trial license any time by sending a short, informal request to support@netikus.net.