In order to use Ink handwriting recognition included with Mac OS X 10.2 you need to install appropriate drivers for your graphics tablet.
Symptom
Ink appears to be ready, but you cannot use it.
Note: Ink does not appear in System Preferences unless a graphics tablet is connected to the computer. The connection of a graphics tablet for which drivers have not been installed may cause Ink to appear, but you still would not be able to use Ink.
Solution
Install the latest drivers available for your graphics tablet.