The default input method for Debian is SCIM. To install iBus, use the following command.

sudo apt-get install ibus im-switch
sudo apt-get install ibus-pinyin # or other engine(s) you want
im-switch -s ibus
# logout and re-login
ibus-setup # add input methods you want

Note:

1. The iBus version is 1.3.7 in the stable distribution("Squeeze"), and 1.4.1 in both testing and sid distribution("Wheezy").