Trouble opening ISO files in UltraISO

I downloaded a program from bittorrent in the .rar format. After uncompressing it, I was left with 3 .dmg files. I need to convert these .dmg files into 1 .iso file. I converted the 3 .dmg files to 3 .iso files using dmg2iso. When I try to open these iso files in UltraISO 5.5 or MagicISO 1.6 they don’t recognize the file. All I get is an error message. When burning an .iso in Nero 6, all I ended up with was a blank cd. Where do I go from here? All I need is the 3 .dmg files to become one working .iso file. Thanks.

Whats the error message? Have you tried opening the dmg files with UltraISO?

Answer: The error message is “Unknown image format!” and the .dmg files wont open either - same message.