The History of Interactive Television

http://technology.guardian.co.uk/online/story/0,3605,468542,00.html
http://www.guardian.co.uk/technology/2001/apr/05/onlinesupplement5
http://tvinteractiva.no.sapo.pt/mba_docs/mba_02.html
http://www.rogertowne.com/InteractiveTV.htm

http://www.itvalliance.org (further down the webpage) http://www.pbs.org/crashcourse http://inventors.about.com/library/inventors/bl_television_timeline.htm
http://filebox.vt.edu/users/rochandl/Network/history.html
The Road to Convergence: Network Transformation and IP

It's reported that Todd Rundgren in 1978 gave the first interactive television concert by broadcasting live over the Warner/QUBE system in Columbus, Ohio (the home audience chose each song in real time during the concert by voting via QUBE’s 2-way operating system). (Reference.)