Hi Carol,
If you want to have a logo appear on all pages regardless of the journal, you'll need to modify the main header template (templates/common/header.tpl) or site-wide CSS file (styles/common.css). The template file is Smarty code, which you can generally modify as if it were standard HTML.
Regards,
Alec Smecher
Open Journal Systems Team
---
Don't miss the First International PKP Scholarly Publishing Conference
July 11 - 13, 2007, Vancouver, BC, Canada
http://ocs.sfu.ca/pkp2007/