mik641,
If your player has a 1.5 inch screen use your need to set the size to 128x96 for widescreen or 128x128 for full screen.
If you have a 1.8 screen use a setting of 160x120.
Here are some links that will help you get the most out of your player.
Using AMV Conversion Tool 3.68
HERE
Full Screen 1.8 AMV
HERE
Pre- Processing
HERE and
HERE