Ditto the file #29-Printing. Takes extremely long for Quicktime to play it, although most times it will. Curiously, its the only title that doesn't have the underscore in it.
Interesting that there have been these playback problems reported - and a couple of others by email. Anecdotally, it seems that G4 Macs are more affected (perhaps exclusively?) than Intel machines.
The H264 codec used for the video encoding is a CPU & RAM hog, that is for sure. So...
The best that I can suggest for Mac users is to reboot the computer (which I know you have done...) and then boot QuickTime Player as the first and only app running, then try to open the videos from within QT Player.
If you still have problems, boot Activity Monitor (in your Utilities folder) and check to see what the CPU & memory usage is. In theory, there should be very little else going on other than QT Player; if there is, it should be recognisable what else is hogging your CPU & RAM.
I will re-encode these few files on the weekend. Unfortunately there is no way to get them to you other than through the full packaged zip files of your order.