Creative Commons have published a Podcasting Legal Guide. Whilst it’s based on US law only, it identifies many issues which need to be addressed if a podcast is broadcast in other jurisdictions.

For example, it discusses the copyright status of unpublished works in the US:

"Every unpublished work from around the world of authors who died before 1936 is in the public domain in the United States. That means that the unpublished diary of an Australian who died in 1930 will be in the public domain in the U.S.; however, that same diary may still be subject to copyright under Australian copyright law in Australia. So, if you are marketing or targeting your podcast for a particular territory, you need to be aware of the copyright laws in that country as well as in the U.S. Moreover, because of the borderless nature of the Internet, you can’t really stop your podcast from distributing to Australia, in which case you may be violating laws in another country."