lanny,
check the main panel.. and look for a wire that is ground.. it must connect to a water pipe somewhere...it should have it.. even older wiring had it... newer code requires a dedicated ground rod 10ft, i think... but older codes had it going to water pipes.
also make sure you arent 'grounding' out to other water pipes in other areas... that will change the nuetral/ground potential...
i am still thinking it is a ballast issue... if possible, run a new circuit, including ground all the way back to the main panel, and then run the ground down to the same ground as the main ground...
and i am thinking of a test for you...
if what you say is true or close to true, then you should be able to charge up the reflector/capacitor, then power down the ballasts and unplug and all that and still read voltage or get zapped, as teh voltage is stored..
but if the voltage is only present when the light is plugged in then it is being induced by magnetic or by high frequency bleed over, as in the article/link i posted...