As long as I have tried, neither the latest Irfanview plugins v.397, nor the latest Zoom Browser v5.8 show the ISO if shooted in Auto/Scene modes.
If you use a scene mode, the iso is set to auto. Consequently Irfanview reports the rather useless "iso=auto". I would recommend to set the mode dial to "P" (for beginners) or Av (for more experienced users) and set the iso to 80 or 100. In this way you get the best image quality. Because the A710 tends to slight overexposure I also set exposure compensation to -1/3. I have never used a scene mode and I only set iso to auto if I need a wider flash range.