Added with version 2.21 was the ability to specify different credentials when using Remote Update. Please see the additional links for more information on this feature.
If you cannot use the built-in authentication feature of EventSentry for some reason and are running Windows 2000 or higher then you can right-click the GUI executable (eventsentry_gui.exe) while holding down the SHIFT key and choose "Run as...". When prompted for a user account specify the account you need to get sufficient access to the remote machines.