[oldfart]

sorted my issues..
you HAVE to
GRANT ALL ON *.* TO 'xbmc';

it does not work if you
GRANT ALL ON `MyMusic%`.* TO 'xbmc'@'%' IDENTIFIED BY 'xbmc';
GRANT ALL ON `MyVideos%`.* TO 'xbmc'@'%' IDENTIFIED BY 'xbmc';

this is not a secure situation - I use mysql on my main server, so am not about to grant xbmc unfettered access to all of mysql

and .. having installed the library, every subdirectory of my media now had loads of files - an nfo file and another 2 jpg files - not impressed.
also, you still have to re-create the library on each machine - not what I expected.

All-in-all a lot of a let down.