Hi boozevixey,
For Carnival in Rio, some events need tickets and some dont. I found this webpage which is very informative about everything-Carnival:
http://rio-carnival.net/
On this web page you can purchase tickets online for Carnival :
http://rio-carnival.net/samba_parade...eservation.php
Have a great time- better start working on your Samba steps now!
Happy Travels,
Lola