The current latest Ubuntu Linux release, 10.10 already has quite rich and complete feature. Hence, to do typing in Chinese character it's quite easy.
The simple tutorial is based on (Gnome) Desktop.
1. Go to System -> Preferences -> Keyboard Input Methods
2. Select 'Input Method' tab when the IBUS Preference shows up, in my case, I select 'Chinese' -> 'Pinyin' then 'Add'.
3. Do a restart on the Input Method Daemon icon -> then you will be able to switch to Chinese input.
(CTRL + Space to switch on / off by default keyboard shortcut)
lastly Happy typing :) 可以在 Ubuntu Linux 系统写中文了 ～