I installed scim-1.4.5,
scim-pinyin-0.5.91 from source. Just the usual
./configure
make
make install

will do.

both can be found at
http://www.scim-im.org/

Then you need a few env. variables set.
I used these by following some of the documentation in that web site I listed:

export LC_CTYPE="zh_CN.UTF-8"
export XMODIFIERS=@im=SCIM #case matters for this variable!
export GTK_IM_MODULE=scim
export QT_IM_MODULE=scim

Then start scim backend by:

scim -d

You may need to reboot after you set those env. variables. It is good idea to put them into some of your startup script so it will automatically take effect.

我还没有弄明白一点， 如果我把LC_CTYPE(缺省locale） 设成 en_US.UTF-8, 中文就不行， 但我的同事可以。
BTW， 我是在Fedora Core 3 上， for other platforms, the website also has instructions.

至于editor, 好像都支持。 反正网页上的输入框， VI， LINUX 命令行(in xterm, or Fedora core's default terminal )都没问题。Just use Ctrl-Space to switch between Chinese and English.