Here is a pack of the current logos for New Zealand TV. The logos are on transparent backgrounds. Simply unzip into the \thumbs\tv\logos directory and ensure they are named the same as your Mediaportal Setup, Television, TV Channels.
The file name of the tv logo must exactly match the name of the channel in TV Server Configuration. If an image is not displaying thats probably the cause.
Place the png image files in
C:\Documents and Settings\All Users\Application Data\Team MediaPortal\MediaPortal\thumbs\tv\logos
Place the png image files in C:\Users\All Users\Team MediaPortal\MediaPortal\thumbs\tv\logos
WINDOWS 7/8/8.1 USERS C:\ProgramData\Team MediaPortal\MediaPortal\thumbs\tv\logos
Updated to be the current logos of NZ channels available on DVB-T and DVB-S as at 20/03/2014.