Quicktime Posterisation Looking problem

[plantphoto]

Hi,
I run a photography training site and been shooting HD video and doing screen capture movies and outputting through quicktime 7.6 (1290).
I had a problem a while ago with video and screencast looking posterized in the darker areas.I blamed imovie 08 and purchased Final Cut Express but I'm still getting it.
My latest HD movie was shot in fading light which I know will not help.
I'm also getting it on my screen casting video especially on a hi res still image I filmed which again has lots of dark areas.
Video is new to me as of 6 months ago so I'm still learning.
My workflow is this.

Shoot HD Video on location (canon HF100) on highest setting.
Import and edit in FCE or Imovie.

Record a screen cast of the retouching of the still image and I output this to apple intermediate codec (i think this is a high quality option)
Current or 15 FPS
Compressor Other
1920x 1200

I then imort this into FCE or imovie and edit together with my HD video I shot.
I then output to
H264
15fps
Data rate 1200-1500
High Quality
Encode Multi Pass

Anyone any idea what if anything I'm doing wrong?
Is there any issues with Posterisation with quicktime?
Also another problem I have is I have tried to output through quicktime to FLV but get error 32766.
Cheers,
Simon
I have uploaded a sample zip if that will help.

http://www.mediafire.com/?cmm1fmymjnu

http://www.ProPhotoInsights.net

http://www.plantphoto.com