Thanks Jason, that worked for the "top level" pages - but those in sub-directories on the site just generate a simailar error message as before:
Warning: require_once(CSSMenuWriter/cssmw_content/menu.php) [function.require-once]: failed to open stream: No such file or directory in E:\domains\b\buytilesbypost.co.uk\user\htdocs\tiles\bathrooms\ceramic2.php on line 98
Fatal error: require_once() [function.require]: Failed opening required 'CSSMenuWriter/cssmw_content/menu.php' (include_path='.;C:\php5\pear') in E:\domains\b\buytilesbypost.co.uk\user\htdocs\tiles\bathrooms\ceramic2.php on line 98
... so any pages on th3e same level as "tiles" are found ok, but anything lower isn't. All the pages other than index.php are generated via a Dreamweaver template.