If you ever need to screencast your desktop to a firewire device - there is an easy way using the Quartz Composer Live DV software.
Thanks to UDART for pointing this out. You need to download the Quartz Composer first. While we are not able to find it on the internet anymore, you may go to UDART for downloading it or directly download it here.
We recently recorded 1000's of lines using voXover. Our voice talents monitor in the voice booth was connected through the composite output of our DVCAM recorder and we needed to find a solution to be able to show the script in the voice booth. Quartz Composer Live DV was the solution.
After unzipping the dv-screen-capture zip file, all you need to do is to drag Quartz Composer Live DV to your applications folder.
When starting your application you should see something like this.
Browse to screen sizes and choose your favorite resolution.
Make sure your hardware dv device is turned on and enable the Firewire Live DV Stream (you can switch between NTSC and PAL). That's all.
If you only see a black screen, you might need to install the v002 screen capture plugin into the /Library/Graphics/Quartz Composer Plug-Ins folder.
If you want to screen cast dv between two macs - follow the tutorial at the UDART blog.