Google QSB plug-in requires Mac OS X 10.5 or later.
You can download the latest version of the Google Quick Search Box here:
http://code.google.com/p/qsb-mac/downloads/list
To install the Things Google Quick Search Box plug-in, follow these steps:
1) Quit Google Quick Search Box if it is already running on your system.
2) Please download and extract the attached plug-in:
Then, copy the plug-in to the Google Quick Search Box folder:
~/Library/Application Support/Google/Quick Search Box/PlugIns
If the folder doesn’t exist, please manually create the folder.
3) Launch Google Quick Search Box.app and accept that the new plug-in is "safe".
Now you can open Google Quick Search Box and enter a string. Pressing tab should now display the new command to create a To Do in Things:
You can learn how to use the plug-in syntax for Things here:
Things plug-in syntax