MHEG is a type of Interactive TV used in DVB. It includes such things as an enhanced channel guide, access to additional video streams, and games. So far the MythTV implementation only contains support for the UK and New Zealand profiles.
New Zealand has also decided to adopt MHEG as part of its FreeView digital platform. They are using a modified version of the UK 1.0.6 profile. Initial support for the NZ Profile is included in 0.21
You can enable Interactive TV via the frontend in
Utilities/Setup -> Setup ->TV-Settings->Playback Onscreen Display. Check the Enable Interactive TV button.
You will get the interactive logo while watching live TV Now while you are watching live TV you can Press F2 on your keyboard to bring up the interactive Menu, and F7 to remove it.