In the Microsoft article http://support.microsoft.com/kb/823586 there are a number of steps to prevent CTFMON from running including:

- Removing Office Components
- Unregistering DLLs
- Removing registry entries
- Running .reg file at logon for users

This may not successfully prevent CTFMON from running, particularly in the event of an Office Service Pack being installed.

The simplest method to disable CTFMON is to deny execute permissions to users at an NTFS level:

XCACLS %SystemRoot%\system32\ctfmon /E /D Users

Frequently asked questions about Ctfmon.exe
http://support.microsoft.com/kb/282599

How to turn off the speech recognition and the handwriting recognition features in Office 2003
http://support.microsoft.com/kb/823586

How to turn off the speech recognition and handwriting recognition features in Office XP
http://support.microsoft.com/kb/326526