There is a typo in the zend_API.h file in PHP 4.0.6 that prevents the ZVAL_TRUE and ZVAL_FALSE macros from being usable in extensions. If they are used without this fix, then the extension won't compile. This fix is in 4.0.7.
Created attachment 29354 [details] patch to fix ZVAL_{TRUE|FALSE} macros
This defect is considered SHOULD-FIX for Fairfax.
This will be fixed in php-4.0.6-7 and later. Thanks!
This was fixed a while ago.