My browser (iceweasel) does include .mov as a supported format. All the files I try to play open a player applet, but it does nothing. Trying to open them manually with Totem results in a "Video Codec Advanced Video Coding (H264) is not installed" error message. I even installed the ffmpeg package - which, for some reason, the gstreamer plugin doesn't seem to depend on...
I'm running a Lenny install dist-upgraded from an Etch install with the desktop task installed.