Hi,
That kind of configuration is completely unsecure. What you want, is opening completely your internal network from DMZ, and this one, by definition, is open to the Internet, then internal nets will be open to the Internet through DMZ servers. Of course, it's possible to do that, but you shouldn't. But, if you absolutely want that config, move your servers to inside and kill your DMZ network, you don't need it anymore. Don't forget, F/Ws aren't miracle box against hackers. They just filtered out some attacks based on the security you have configured on it. Then, f/w is as good as the person who has configured it.
If you want some advices on this subject, you can contact me directly.
Ben
