Matrox MX02 Mini has HDMI in (MXO2LE add HD-SDI) going into MacBookPro with Express slot and Wirecast to add overlays PiP etc.
MXO2Mini is about $449 (give or take).
You can do this without Wirecast (just Adobe Flash Media Live Encoder) but Wirecast gives you a professional front end
http://forums.creativecow.net/telestreamwirecast
and
http://www.telestream.net/wire-cast/overview.htm
also COW Matrox forum
http://forums.creativecow.net/matroxvideosystems
and Matrox MXO2 Mini
http://www.matrox.com/video/en/products/mac/mxo2_family/mxo2_mini/
