function rollimg(img_src)
   {
   document["main_img"].src = img_src;
   }
function rollimgL(img_src)
   {
   document["main_img"].src = img_src;
   document["main_img"].height = "300";
   document["main_img"].width = "450";
   }
function rollimgP(img_src)
   {
   document["main_img"].src = img_src;
   document["main_img"].height = "450";
   document["main_img"].width = "300";
   }
function rollimgX(img_src, img_w, img_h)
   {
   document["main_img"].src = img_src;
   document["main_img"].height = img_h;
   document["main_img"].width = img_w;
   }