Replying to MAC PROBLEM: HELP

Howdy yall. I have an imac 1.8 ghz intel core duo processor, and Im having a problem with torrents.

I torrented this application, unstuffed it, and it gave me a .dmg file. When I try to open the dmg and mount a disk image, it gives me an error saying no mountable file systems. I've tried using disk utility to mount it, and I tried creating a new disk image and then transfering the files, but neither works. I also tried converting to to a .cdr file and burning it to a cd in order to create a disk image, but it didnt work either. I have a suspicion that the image that its supposed to mount is related to titanium toast, which I dont have, except for a really old and out of date version (toast 5, new one is 8). WHAT CAN I DO?