change:
<?php virtual("/CSSMenuWriter/cssmw_home/menu.php"); ?>
to:
<?php require_once("CSSMenuWriter/cssmw_home/menu.php"); ?>
Dreamweaver is using the "virtual" syntax because in your Site Definition, the "Create Links Relative To:" option is set to Site. If you change that to "Document" instead, Dreamweaver will use the "require_once"syntax.