I decided to give Video Lan Client a try. This application not only could play the DVD, but I discovered that I could capture frames using "Grab" (in Applications -> Utilities) which I could not do using the DVD Player ("Grab" will complain and not launch if the DVD Player was previously launched).
In order to capture a frame, I first pressed the space bar in VideoLan Client to pause the palyback, then proceeded with the capture with "Grab". I tried both area capture and full screen capture successfully.
[Editor's note: I haven't tried this program myself, but it appears that it works around the ATI vs. NVidia problem (ATI cards can't capture DVD screens; NVidia cards can when using SnapzPro), as the PowerBook 400 shipped with an ATI card. I'm also not sure if VideoLan Client can handle all DVDs or not -- anyone have more experiences to share about the program?]

