I too would like to know more about these lights. You could be talking about low voltage halogen, regular voltage halogen, or even can (recessed) lights. You might even be talking about surface mount fluorescent lights that just plug into an outlet.
No matter which you choose, the ceiling panels will not support them. The grid may be strong enough, but you may need additional support to the joists. If you want them centered in the panel, you'll need to install blocking, attached to the joists, to support the lights. A small fluorescent light can be supported by the grid.
Why not staple the wires to the joists? Even if its one of those fluorescent fixtures I'd run the cord up to the joists and back down the wall. If you need to run an extension cord, you're better off having an electrician wire an outlet on a joist next to the light. With a suspended ceiling, the outlet is still easily accessable.