VECTOR vMax, vMin;
vec_set ( &vMax, vector(400,200,200) );
vec_set ( &vMin, vector(0,0,0) );
VECTOR vCenter, vBounds;
vec_lerp ( &vCenter, &vMax, &vMin, 0.5 );
vec_diff ( &vBounds, &vMax, &vCenter );
...
VECTOR vP1, vP2;
vec_set ( &vP1, &vBounds );
vec_set ( &vP2, vector(vBounds.x,-vBounds.y,-vBounds.z) );
vec2d_rotate ( &vP1, nRotation );
vec2d_rotate ( &vP2, nRotation );