Group Video Conferencing on an XP LAN

Hi All

Basically I work for a number of schools and they want to video conference
an 'author' (really a teacher) with 2 or 3 classes at the same time on the
LAN.

The idea would be that the author hides in the staff room with a laptop,
webcam (?) and headset (?).

The classrooms' PCs, which are hooked up to a interactive whiteboards, would
have a webcam and microphone (??) setup.

Each classroom would see the author projected on the smartboard in full
video and would hear him through the audio speakers.

The author would see a video 'window' of each classroom so he can see what
they are doing.

The children in the classrooms would ask him questions via their classroom
mics and the author would reply back.

It only seems like I need say 1 x headset, 2 x good microphones and 3 x web
cams, but what software could do this?

There seems to be loads of web cam software, but none that covers this
requirement. Anybody got any ideas?

Thanks

Robbie