Alright, I tried using the original CD now but the problem stays the same. The game still tells me there is no CD of the game being found.
I set the CD\DVD-settings to superdrive which lets Windows 7 read the drive in my MacBook but still, the CD works nicely and is displayed correctly yet if I try starting the game, the same error keeps appearing. So I guess the iso files weren't the problem because they worked just like the CD itself.
The problem does not appear when I try playing the games on my Windows Vista Laptop, though. So the CDs actually work.