His early stuff is definatly out of copyright
(Gymnopedies and
Gnossiennes were pre- 1900) - I think the cutoff is 1923 (its the
creation date of the The Mouse), but I should check that.
According to this article:
http://www.artquest.org.uk/artlaw/articles/thelenghtofcopyright.htm
in the UK it's author's death plus seventy years, so if the 1925 date
is correct then everything he wrote went into the public domain in
1995. Apparently it used to be death plus fifty, but it was extended
by the EU to harmonise with German law.
So that means if I release a piece of music today and I live to be
100, it will enter the public domain in the year 2142. I expect I'll
have milked every last eurocent from the composition by then...
Cheers
Daniel