Although I got my 64MB-Memorystick DUO today finally, I decided to use OGG for playback, because it should aprox 200% of space utilization against MP3 with similar results... P800 Ogg Vorbis Player is available in a V0.7 beta and works fine even with closed keypad... and it's free (open-source)...

Encoding was a bit fancy, because there are commericial tools available ofcourse, but a free MP3-to-Ogg converter in form of the FileWriter-Plugin for WinAmp by Jasper. This is wonderful, because I can use my musicplaying-tool now for converting some stuff (whatever format) to ogg and need no additional tools (or fees)...