Let me tell you a simple way of getting the CAPS, not playing the whole BD. First, you have to install windows or use some PC, RIP with  ANYDVD HD then you can just grab the movie mts file and play it with a  "OS X" VLC INTEL Night Builds:

http://nightlies.videolan.org/build/macosx-intel/

The image will probably look better than most Windows softs because  VLC for Mac uses the improved H.264 processing and acceleration. You can also download Perian QT Codec Kit and try to play it with Quicktime. Mac Sure you also install the Toast Titanium BD/HDDVD  Plugin. It is PAID! You can also play the MTS with the Toast Player,  but i don't like it. But the plugin improves compatibility and also  allows some extra sets for export.

http://perian.org/#download

http://www.roxio.com/enu/products/toast/plugin/overview.html

Or you can just install all the codecs I specified (below) to you for windows  and play through VLC on Windows itself and take the grabs from it. If you install all those codecs you will be able to play the DTS-HD  mixes, the Dolby TrueHD mixes and even use a subtitle you downloaded from the internet while playing the Blu-ray.

You NEED A INTEL MAC - iMovieHD is a recommended install! And having  Final Cut Studio (my case) Install may help as well, since it comes with more codecs to work with AVCHD.  But i really don't know if it  helps much, and i mostly use VLC anyway.

You can also use some conversion tools: http://www.moviesmac.com/video-converter-mac/

But they are pretty stupid, you should be able to do well with QT and  VLC. Make sure you have a lot of free space 100GB if you are going to use Quicktime for anything.

Anyway, DTS-HD and Dolby True-HD sound in a Mac OS X system is  problematic, some times it works with VLC sometimes it don't. So you  may stick with playing t through Windows if you want to be sure your  DTS-HD sound will play smoothly.

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I always use VLC on Windows Vista to play the ripped BDs, but I install a bunch of codecs. The quality is better than PowerDVD that can also be used but i am not sure if the quality will be the same, I believe it won't.

Among the codes I use : CoreAVC Pro / Mainconcept Reference / Ac3Filter / DirectVobSub / ffdshow / AviSynth V2.57 / HD DVD decoder

I think that for screenshots alone, AnyDVD HD + VLC + "K-Lite Codec Pack" (free) will do the job and it is easy. He can also use PowerDVD 7.3 Ultra or a new version and take the screenshots (quality may be compromised) as well, or just Avisynth to capture the frame and another player that can be WMV to save the screenshot. But the avisynth may look like a more troublesome way.