I am not a coder by any means, but I couldn't find an AppleScript to turn on and off trackpad clicking. On my ibook, I usually have trackpad clicking on, but when I'm doing alot of typing I like to turn it off. So I wrote this very brute force UI script to do just that. Feel free to offer improvements (such as more elegance and perhaps running in the background).
tell application "System Preferences"
activate
set current pane to pane "com.apple.preference.keyboard"
tell application "System Events"
keystroke tab
keystroke (ASCII character 29)
keystroke space
keystroke tab
keystroke tab
keystroke tab
keystroke space
end tell
quit
end tell
[robg adds: To make it easy to use this script, you could save it in your user's Library: Scripts folder, and then access it through the Scripts icon in the menubar...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050303134503678