Sadly, the HD 4xxx series does not have particularly good power saving features in the Open Source driver today, let alone when this question was written.
Unless the card was designed to run with the fan off, it will not be able to run at all without it. Additionally, most AMD cards contain firmware that regulates the fan. I would not recommend forcing off the fan, but instead simply relying on the card's internal firmware to regulate the fan speed.
To reduce the fan speed, you would need to simply reduce heat production. I would recommend reading up on the latest power save options to force the card to remain at minimal clock speed. This will give you decreased heat production at the cost of decreased performance.