Check out this web site re rail travel in Europe. http://www.europeanrail.co.uk/fs_home.htm

A for day trips out of Paris, I suggest you take a train here and there to different places and organise it yourself. You can see what you want to see and you can keep cost down. Although if you are only going to be in Paris for 5 days, I doubt if you will have time for that.

Happy planning!!

Regards,

Bard Vos Arroyo de la Miel - Costa del Sol (Spain) http://www.apartamentosmundial.com