I found this thing about a time capsule (space craft) that will be launched in 2009/10. It is called KEO and will carry up to 6 billion individual human messages from everyone on the planet (if they can collect them) into space only to return in 50 thousand years. It will also carry human blood, current samples of the air, water etc.
If you want to read up more go here
and to leave a message for the future go here
Im pretty sure its for real.