Daemon Tools Light is also a free utility you can download and use to mount .iso disk images to play in PowerDVD and other software players. Once you install that utility, it will be clear how to actually mount the .iso as a drive.
DVDFab Virtual Drive is what I used to use. It's a free. Once installed, you just right click on the .iso and "mount to (drive letter, usually H: )" and then when you open up TMT5, it'll be the drive or icon on the far right (of the 3 icons that would be displayed - BD player, HDD, Virtual Drive)