Unrecognized ISO?

[Pants Dragon]

I'm trying to mount a series of 4 ISOs, and when I try to mount them it fails and gives the reason "not recognized". They were sent to me by a friend who uses Windows, but I believe ISOs are supposed to be universal, since I've mounted them before. Any idea as to what the problem could be?

 

[Frida]

What machine and system are you running? Have you tried mounting them from within Disk Utility? Are the ISO's actual discs or only disc images?

 

[Pants Dragon]

Mac Pro (Intel Quad Core 2.66Ghz)

I tried within Disk Utility but it didn't work. I've gotten the files as dmgs which work now though, so I don't need any more help, although it is still puzzling why the originals didn't work.