A number of years ago, when Havok was owned by Intel, they offered a binary distribution for Windows. Intel sponsored this as a marketing tool to help promote the sale of Intel processors, and to fight the idea of GPU-accelerated physics such as PhysX (which leverages NVidia's CUDA).
When Microsoft purchased Havok, they discontinued the program as they surely felt it was not in their best interest to give the product away for free.
As a result, the only way to use Havok is to purchase it. This is done by contacting Havok, and entering into negations with them.
In contrast, a product like Bullet is free for use. It might be a better option for you now that Havok is unavailable.