You should use shaders. No idea how that works, but the got it working with havok. But GPU is only for simple physics. You can calculate +10.000, but al in a simple way. It you really want to have a large scale I suggest to take a look at agiea physics engine. They also make the hardware. And if ist only server-side, the only one needing a physics card is the server. (they cost around $250 I think)