After 2 hour searching
fixing it :
in php.ini : option log error in a file (don’t remember the exact syntaxe)
-> log_error : On
-> specify a filename for logerror some line after
done.
restart a fresh install
worked with a 2.5 rc1 + php5 + mysql5
Brievly: it seems that if php do not log error in a file , wordpress won’t install
