[ODE] Object speed

[Geoff Carlton]

Why not just use the proper equation:
    v = dBodyGetLinearVelocity(body);
    speed = sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);

If the sqrt is too slow then you could consider using the squared speed, 
or else a fast sqrt approximation function.

Geoff