Thanks a lot to phreakymonkey for this tutorial.
Screen Capture in OS X
To quickly take a fullscreen screenshot in OS X, hit CMD-shift 3.
Probably more useful for the purposes of these riddles will be the . Type CMD-shift-4, and a crosshair cursor will appear. Use it to select an area of the screen. When you release the mouse button, a screenshot will be taken. Alternatively, press spacebar to turn the crosshair into a camera and click on a window to capture it.
By default, screenshots in OS X are saved to the desktop as Picture n.png
More detail on OS X's built-in screenshot abilities may be found here.
edit: Submitted by user Ahem
I thought of another helpful trick for Mac users, though I don't know if it's to obvious to be listed or not.
In Mac OSX you can zoom in on anything on the screen. All you need to do is go to System Preferences>Universal Access>Zoom On
Then, at any time, you can zoom in on what your mouse is hovering over by pressing option-apple-+ (to go back to normal size you press option-apple--).
Note: you can also turn on zoom with the keyboard by pressing opt-apple-8.
The GIMP (Freeware)
If you don't already have Photoshop and can't afford to shell out several hundred dollars for it, check out the GIMP.
There are also tutorials available for the GIMP here.
Audio Hijack (Shareware)
This is a great application for ripping audio from applications. It can capture from about any application you throw at it, and the unregistered version is fine for capturing up to 10 minutes of audio. Should be more than sufficient for this game.
Ironically, despite having piles of professional sound editing software, this freeware application is proving itself infinitely more useful. I am growing to loathe Pro Tools, Peak, DP, Soundtrack Pro, for missing some extremely basic features. Audacity is simple, easy to use, and can do all you need for this game (so far as I know). A lovely little piece of software.
Hex Fiend (Freeware)
A mac-specific, universal binary app.
An older, less supported app, but a classic.
There are some riddles that are aimed more specifically for the PC crowd. Take a look at the following. There is a chance they will makes things a little less confusing at points. I won't tell you when they'll help, and you may not need them at all, but just in case...
8th february 2013: i'm sorry to realize that these hints are not available online anymore; i have no copy of it... (edit by bacchus)