> tr.style.display = none;

(Ahem - quotes.)

Setting it back to shown is more difficult. It should be done by setting
display to 'table-row', but IE/Win doesn't understand this - you have to
use 'block' instead. Which of course would break other browsers. So:

  SHOWROW= 'table-row';
  if (window.clientInformation && navigator.platform.substring(0,3)!='Mac')
    SHOWROW= 'block';


  tr.style.display= (showFlag) ? SHOWROW : 'none';

(As usual, not tested in - and probably will break - IE/Mac...)