I'm pretty sure you could put things like the national anthem or Bach in some of your own productions. You should of course make it clear who has composed the music and not make any direct profit from it though.
Look at my thread "Gammal Fäbodpsalm" on this board; I have recorded it but I definitively don't claim to have written it. I also have put the composers name in the artist tag of the file.
This is most probably ok, seeing as this is a well known religious song that has been around for ages.
There is even a guy who have made profits from remixing this song, so that seems to be ok too, but I wouldn't do that.
"I kören hörs de brummande busarna Björnligan och Gondolen"
