if( document.images ) {
   var but01on = new Image(); but01on.src = "img/but01_over.jpg"
   var but01off = new Image(); but01off.src = "img/but01.jpg"
   var but02on = new Image(); but02on.src = "img/but02_over.jpg"
   var but02off = new Image(); but02off.src = "img/but02.jpg"
   var but03on = new Image(); but03on.src = "img/but03_over.jpg"
   var but03off = new Image(); but03off.src = "img/but03.jpg"
   var but04on = new Image(); but04on.src = "img/but04_over.jpg"
   var but04off = new Image(); but04off.src = "img/but04.jpg"
   var but05on = new Image(); but05on.src = "img/but05_over.jpg"
   var but05off = new Image(); but05off.src = "img/but05.jpg"
   var but06on = new Image(); but06on.src = "img/but06_over.jpg"
   var but06off = new Image(); but06off.src = "img/but06.jpg"
   var but07on = new Image(); but07on.src = "img/but07_over.jpg"
   var but07off = new Image(); but07off.src = "img/but07.jpg"
   var but08on = new Image(); but08on.src = "img/but08_over.jpg"
   var but08off = new Image(); but08off.src = "img/but08.jpg"
   var but09on = new Image(); but09on.src = "img/but08_over.jpg"
   var but09off = new Image(); but09off.src = "img/but08.jpg"
   var but10on = new Image(); but10on.src = "img/but08_over.jpg"
   var but10off = new Image(); but10off.src = "img/but08.jpg"
 }

function imgon( name ) {
  if ( document.images ) {
    document[ name ].src = eval( name + "on.src" )
  }
}

function imgoff( name ) {
  if( document.images ) {
    document[ name ].src = eval( name + "off.src" )
  }
}