Chap, good work!
Check this out. Currently working on updating it so I can use it with my new USB bullet cam for Wales. Was going to make it into a CF plugin, but that looks like a mission. The plan is to get it working with speed overlays etc.
http://www.mp3car.com/vbulletin/softwar ... rding.html
Jump to the last page, thats where the last updates are. I can give you a copy of my local dev version if you want, I got it working quite nicely. About to send it over to Prefect for his approval.