dBodyAddTorque axis problem

[phoenix]

i have a chase camera that looks at a sphere from some distance. to
giv u an idea this is what i am using

gluLookAt(pos[0] - 10*lx , pos[1] - 10* ly , pos[2]-10*lz, pos[0],pos
[1],pos[2],0,1,0);

lx,ly,lz defines line of sight.

i wanted to add torque to the sphere. when i pass lx,ly,lz as axis it
rotates correctly to the right.from what i read i need to pass the
axis around which torque is to be applied. can anyone tell me how can
i calculate the vector, around which the sphere will roll ahead in the
direction of the camera facing. the vector should be parallel to x-z
plane.