Hello Merlinpa. I managed to remove the ZenCart logo by following your instructions ie. placing <!-- at start and --> at end of the code you stated.

After that I inserted my own company logo by naming my logo as logo.gif and changing header.php as follows :

// added defines for header alt and text define('HEADER_ALT_TEXT', 'Cable Master :: Cabling Professionals at your Service'); define('HEADER_SALES_TEXT', 'TagLine Here'); define('HEADER_LOGO_WIDTH', '235px'); define('HEADER_LOGO_HEIGHT', '50px'); define('HEADER_LOGO_IMAGE', 'logo.gif');

but I still get the ZenCart logo in my site cablemaster.com.sg/ecable/