flash = false;
if ((navigator.plugins) && (navigator.plugins.length > 0))
{
   for (a = 0; a < navigator.plugins.length; a++)
      if ((navigator.plugins[a].name.indexOf('Flash') != -1) &&
          (parseInt(navigator.plugins[a].name) >= 6))
      {
         flash = true;
         break;
      }
}

// alternativ, testet nur auf beliebige Version (>2?):

if ((navigator.mimeTypes) && (navigator.mimeTypes.length > 0))
   for (a = 0; a < navigator.mimeTypes.length; a++)
      if (navigator.mimeTypes[a].type.indexOf("application/x-shockwave-flash")>= 0)
         flash = true;