DVD playback on my PC seems to be slow/stuttering

You might want to consider dropping the screen resolution to 800x600 on your desktop. This doesn't cause a drop in video quality at all, as the maximum resolution of DVDs is 720x576 (PAL) / 720x480 (NTSC). Also, close all the other applications while watching the DVDs. If this doesn't help, you might consider upgrading your PC :-)