His laptop fell off the car and got run over. He was given this mini to use which did not have 10.4. This is a Macmini G4 1GB RAM running 10.4.11 with all current updates. iLife 08 installed. iMovieHD6 version 6.0.4 installed from my backup copy which I had downloaded from Apple because version 8 does not install on PPC. I completely wiped the drive and did a fresh install of 10.4. And then initialized the system.I then installed iLife08, then iMovieHD6. He has QT Pro also probably 7.6.2, the same one I have.

Hey mom, I have been having a problem with iMovie since we upgraded my
system. Could you ask the Mac Users Group? Here's the situation:

When I try to play quicktime movies on my machine that I've exported
from a newer version of iMovie, all I get is the audio, no video, and
this message: "Additional software is required for QuickTime to
playback this media. It may be available from the QuickTIme
Components page." There are a lot of components, and I've done a
search online, but can't seem to figure out what I'm missing.

Also, I have iMovie HD 6 and when I import video into iMovie from the
files my videographer gave me, then same files I used earlier in the
year to create the first five videos from the January show on this
very computer, it does the same thing - no video, only audio. And of
course as I type you this, I can get Video on one of those files, but
it also goes to total black if I set the playback head to zero and
start from there. Weird. Oh... and now that I've told you that, the
gremlins have decided that no matter what I do I can't see the video,
just audio again now.

Info on my machine:
OS 10.4.11 build 8S165
1.42 GHz PowerPC G4
1 GB DDR SDRAM

Quicktime movie info (they're all like this):
720x480
Integer (Little Endian), H 264, Hint
Channel Count: 2

Uncompressed Files:
720x480
Codecs: DV/DVCPRO - NTSC, Integer (Little Endian), Timecode
Channel Count: 2

Any hints?

What version of QuickTime is on the machine? "Probably" isn't good enough - we need to be sure.

It sounds like a codec is missing. I would install (or re-install) the current QuickTime for starters.

To reinstall should we Trash the current version first? Then download fresh from Apple and reinstall?

I would just download and run the installer.