var revert = new Array();
var inames = new Array('Btn1_', 'Btn2_', 'Btn3_', 'Btn4_', 'Btn5_', 'Btn6_', 'Btn7_', 'Btn8_', 'Btn9_', 'Btn10_', 'Btn11_');

// Preload
if (document.images) {
  var flipped = new Array();
  for(i=0; i< inames.length; i++) {
    flipped[i] = new Image();
    flipped[i].src = "Btn/"+inames[i]+"2.gif";
  }
}

function over(num) {
  if(document.images) {
    revert[num] = document.images[inames[num]].src;
    document.images[inames[num]].src = flipped[num].src;
  }
}
function out(num) {
  if(document.images) document.images[inames[num]].src = revert[num];
}