There are at least two different techniques available for accomplishing what you want.
The first technique is to use a tool that can open the image file itself, and show you what's inside. IsoBuster is a Shareware/Freeware tool that can accomlish this, and you can do this with the Freeware license. Another tool that can do this and much more is UltraISO which is a Shareware program.
The second technique is to use a Virtuel CD/DVD drive emulator and then "mount" your image as a virtual CD/DVD on the virtual drive. If you have the full Nero suite, you can install the Nero ImageDrive option which is capable of handling ISO and NRG images. There's also Alcohol 120% (commercial software) which is a full-fledged Virtual CD/DVD drive emulator. And there's DAEMON Toolswhich is a free Virtual CD/DVD drive emulator.