Try using keyboardredirect.ahk. It will maintain keyboard focus on whatever window your mouse cursor is over. If you click and start typing in a chat/note window, no other windows can steal focus.
Download and Install Autohotkey -
http://www.autohotkey.com/
Then download (right-click > save link as...) and run this file -
http://dl.dropbox.com/u/11623474/Key...rect-v0.01.ahk
You should see a green 'H' square icon in your tray to indicate it is running.
If you have any problems downloading the .ahk file:
Download this zip file -
https://dl.dropbox.com/u/11623474/Ke...-v0.01.ahk.zip
Unzip the file to a new folder: Right-Click > Extract All
Double-Click the extracted .ahk file