The Site Administrator role is the only role that can not be granted via the web interface. Typically there is only one admin account per installation, created at the time of installation, but if you want to grant an additional user admin privileges, you can insert the role manually into the database in the roles table using a journal_id of 0 and a role_id of 1.
Open Journal Systems Team
Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada