Sorry it took so long to respond. To test the wires at the box, do what crafter_man suggested in his post.
You may find that they are switching the nuetral, they did this in the old days.
Most likely they are switching the hot. The hot wire should be the darker of the two (usually black). The nuetral should be the white (or grayish, depending on the age of the wires).
If the box is grounded (testing from the hot to the box gives you 120v., or continuity between the nuetral and the box is 0 ohms) then the following should work for you…
The box itself should have a threaded hole in it for a #8 grounding screw. If it doesn`t and you still want to ground the fixture get a self tapping #8 screw and use a screw gun to drill it into the back of the box. Being careful not to drill into any wires or cables. Then take a length of solid bare wire and wrap it around the screw, then tighten the screw. Wire nut the other end of the wire to the copper lead from the fixture.
I believe all fixtures come with a ground wire these days… how would the manufacturer know where you are going to put the fixture?
Q.E.D. this is a flourescent fixture, so there will not be any screws. There will be wire leads of black and white however (and green or copper for ground).