Presently on this site, JVC Introduces GY-HM700 ProHD Camcorder (http://www.videography.com/article/79250) when you first log on, a guy wanders in bottom right and chats for a while. The webpage remains visible behind him as he does so!

Any thoughts on how this is achieved?

(By the way, I'm not sure if he reappears on multiple visits to that url ...)

Green screen shooting, then export with On2 VP6 codec with transparency enabled.
Then playing on the web page with flash player.
There are tons of website doing this and many companies offering this service.

Do you mean the scripting side or the production aspect?
Its been awhile but I remeber flash has 2 codecs (sorenson & On2) Sorenson is poo and i dont think anyone uses anymore.
On2 allows you to export .FLA videos with transparency, you have to check 'encode alpha channel'. A web designer can easily add Flash videos to a website.

> On2 allows you to export .FLA videos with transparency

That's the answer I was looking for! Thanks!