With so many 'good' ISO image reading apps out there, I doubt we'll see Opus integrate this functionality, but it's worth submitting a feature request. Personally, I've never had any reason to use any program other than Daemon-Tools. Aside from the manual commands that Ghostrider mentioned, it's also pretty easy to hook into the nifty awxDTools shell extension that arniWORX wrote for Daemon-Tools if you go with that program. If you're not aware, it 'mounts' a selected ISO image file as a virtual optical drive letter which you can then browse directly as if it were a real DVD/CD.