As already said, you can't use PHP in templates (except a few functions in <if ...>-statements.
What you can do is put code in phpinclude_start|end, you can also do this conditional by using
PHP Code:
if (THIS_SCRIPT == 'foobar') {
// Do smth for that specific page
}
Modifying vB so it is possible to use PHP in templates generally is a bad idea due to security issues.