total_images = 40;
use_count = 5;
images = new Array(total_images);
used_imgs = new Array(total_images);

for (i = 0; i < total_images; i++) 
{
  used_imgs[i] = false;
}

images[0] = "<img src='thumbs/thumb_01.jpg' border='0' width='20%'/>";
images[1] = "<img src='thumbs/thumb_02.jpg' border='0' width='20%'/>";
images[2] = "<img src='thumbs/thumb_03.jpg' border='0' width='20%'/>";
images[3] = "<img src='thumbs/thumb_04.jpg' border='0' width='20%'/>";
images[4] = "<img src='thumbs/thumb_05.jpg' border='0' width='20%'/>";
images[5] = "<img src='thumbs/thumb_06.jpg' border='0' width='20%'/>";
images[6] = "<img src='thumbs/thumb_07.jpg' border='0' width='20%'/>";
images[7] = "<img src='thumbs/thumb_08.jpg' border='0' width='20%'/>";
images[8] = "<img src='thumbs/thumb_09.jpg' border='0' width='20%'/>";
images[9] = "<img src='thumbs/thumb_10.jpg' border='0' width='20%'/>";
images[10] = "<img src='thumbs/thumb_11.jpg' border='0' width='20%'/>";
images[11] = "<img src='thumbs/thumb_12.jpg' border='0' width='20%'/>";
images[12] = "<img src='thumbs/thumb_13.jpg' border='0' width='20%'/>";
images[13] = "<img src='thumbs/thumb_14.jpg' border='0' width='20%'/>";
images[14] = "<img src='thumbs/thumb_15.jpg' border='0' width='20%'/>";
images[15] = "<img src='thumbs/thumb_16.jpg' border='0' width='20%'/>";
images[16] = "<img src='thumbs/thumb_17.jpg' border='0' width='20%'/>";
images[17] = "<img src='thumbs/thumb_18.jpg' border='0' width='20%'/>";
images[18] = "<img src='thumbs/thumb_19.jpg' border='0' width='20%'/>";
images[19] = "<img src='thumbs/thumb_20.jpg' border='0' width='20%'/>";
images[20] = "<img src='thumbs/thumb_21.jpg' border='0' width='20%'/>";
images[21] = "<img src='thumbs/thumb_22.jpg' border='0' width='20%'/>";
images[22] = "<img src='thumbs/thumb_23.jpg' border='0' width='20%'/>";
images[23] = "<img src='thumbs/thumb_24.jpg' border='0' width='20%'/>";
images[24] = "<img src='thumbs/thumb_25.jpg' border='0' width='20%'/>";
images[25] = "<img src='thumbs/thumb_26.jpg' border='0' width='20%'/>";
images[26] = "<img src='thumbs/thumb_27.jpg' border='0' width='20%'/>";
images[27] = "<img src='thumbs/thumb_28.jpg' border='0' width='20%'/>";
images[28] = "<img src='thumbs/thumb_29.jpg' border='0' width='20%'/>";
images[29] = "<img src='thumbs/thumb_30.jpg' border='0' width='20%'/>";
images[30] = "<img src='thumbs/thumb_31.jpg' border='0' width='20%'/>";
images[31] = "<img src='thumbs/thumb_32.jpg' border='0' width='20%'/>";
images[32] = "<img src='thumbs/thumb_33.jpg' border='0' width='20%'/>";
images[33] = "<img src='thumbs/thumb_34.jpg' border='0' width='20%'/>";
images[34] = "<img src='thumbs/thumb_35.jpg' border='0' width='20%'/>";
images[35] = "<img src='thumbs/thumb_36.jpg' border='0' width='20%'/>";
images[36] = "<img src='thumbs/thumb_37.jpg' border='0' width='20%'/>";
images[37] = "<img src='thumbs/thumb_38.jpg' border='0' width='20%'/>";
images[38] = "<img src='thumbs/thumb_39.jpg' border='0' width='20%'/>";
images[39] = "<img src='thumbs/thumb_40.jpg' border='0' width='20%'/>";

i = 0;
while(i<use_count)
{
  index = Math.floor(Math.random() * images.length);
  if (used_imgs[index] == false)
  {
    used_imgs[index] = true;
    i++;  
    document.write(images[index]);
  }
}
