I upgraded by xubuntu notebook to 11.10 and accents in my brazilian keyboard no longer work. They work neither in the basic Brazilian keyboard layout nor does the compose key work in the nodeadkeys layout.
Xfce Goodies Project has a plugin that allows you to setup and use multiple keyboard layouts:
Install and use it to change you keyboard layout to Brazilian.
There's a known bug where users report that the plugin resets all the settings (languages used and a switch layouts hotkey) every time the system gets rebooted.
If it happens to you, there's already a work around at this askubuntu answer.