Is this possible - Video/Internet

[spaceman]

I know there are software packages like Visual Communicator that will
let you stand in front of a green screen and then show you in front of
a different background for the PC.

I would like to create a website where people (in real time) can do
small music performances or anything else in front of different
backgrounds or even cartoon backgrounds created with something like
Flash.

Is this possible using Java or any other language on the Internet? Or
is this something that can only be done on home pc and then manually
mapping it on top of a background. Because I really want this to be
done real time.

Thank you,

Markis