Unfortunately Trailmap stopped working ages ago.  What's the easiest way now to get a Google Earth image suitable for a Garmin GPS?

Thanks, no I've not used Mobac at all.  After a few hours Googling etc and getting pretty much over the limitations of Custom Maps anyway (the tile limit and slow screen response) I eventually figured out how to patch the firmware on the 78s GPS so that it could display BirdsEye images downloaded for another GPS - in this case a 64s that comes with a 1 year subscription for BirdsEye.

As the BirdsEye interface is pretty clunky with minimal instructions / support another method was found in SAS.Planet.  This is a Russian based programme, free with an English interface and an English section on the user forum.  This programme is capable of generating the BirdsEye type of file (.jnx) from a wide variety of sources, mainly Europe / US coverage.

For NZ I found that the area of Google Satellite imagery I was trying to download (Big Ben, south west of Lake Taupo) became very blurry over a large area around the mountain so it was unusable.  All other areas on NZ and the world are the normal good detail.  I think they take a dim view of actually downloading their data so will have to try from a different computer / router (guessing here).  The Bing satellite images were not too bad but not evenly coloured so the next was ESRI > Arc.GIS Terrain.  This was an even colour and a good sized area covering about 5km NSEW of Big Ben was converted to .jnx format and loaded to the GPS.  The idea was to show the bush clearings and I hope the data is not too dated. 

Have also downloaded Mobac just now and will look into that further.  Thanks for the tutorial!

10 mins later ... Nokia Satellite and Ovi Sat look darn fine alternatives to Google Satellite!

Yes, the jnx files seem to pan very quickly.  Am downloading more of the SI at the moment so will try it out and time how long it takes to pan from coast to coast at a certain zoom level once the files are on the 64s.

The maximum area that can be downloaded for each tile at their highest quality setting is about 254 sq. km which is about 15,500 images.  The tile file size limit is 233MB. 

The shape of the tile can be a square / rectangle or can be hand drawn with click and drag of the mouse so this is convenient to avoid getting too much ocean.  However the dialogue box does not show the selected size until the hand drawn shape is closed (the end joins up with the start) which is a bit of a nuisance as if the bounded area is too big there's no fine adjustment - you have to redraw it again.

Here's Mt Fell Hut (near Wairau River, South Island) with the Open Project Topo v12 map switched on in BaseCamp:

You need a valid subscription to Garmin Birdseye for *.jnx files to work.
The other option to get them to run is to patch/hack your firmware, then they will run and it won't care where they came from.

JNX Info Here
Some Patcher Info Here   
More Patches / Maps e.t.c 

Remember!......Buy em if you like em! So they can afford development 
No doubt they are already feeling the pinch of waterproof smart phones with better screens and better maps 
Android : BackCountry Navigator
iPhone : Galileo

Garmin 64/64S JNX Patch : Here

NOTE: THIS WILL STUFF YOUR WARRANTY