Sophie, I was able to make and customize pages. Only, it seems that PHp session variables cannot be read.
Example: this line of code at the beginning of the template <?php $g_ui_locale=$_SESSION['g_ui_locale'];?> does not get any value. Obviuosly, PHP in custom pages is enabled (allow_php_in_site_page_templates = 1 in app.conf).
Any hint? I am working with pawtucket2 v. 1.7.8.
oops... found trick... just put before using the variable the statement: global $g_ui_locale;