My original post on this was faulty! While the registry entries needed for Word to know about the add-in were moved into the "All Users" domain, key registry entries for COM were not. My apologies to those who tried the original solution, and got frustrated when it didn't work.
Below is the complete set of registry entries needed to get the International Character Toolbar working for All Users in Word. Copy the text into Notepad. There is one small edit to be made. The portion of the line highlighted in red needs to be changed to the full path of where you installed ICT to. Save this file with an extension of .reg, locate it in Windows Explorer and double click it.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\Software\Classes]
[HKEY_LOCAL_MACHINE\Software\Classes\ACT.Connect]@=""
[HKEY_LOCAL_MACHINE\Software\Classes\ACT.Connect\CLSID]@="{4899F9F9-3960-4768-B17E-09AC400164A5}"
[HKEY_LOCAL_MACHINE\Software\Classes\ACT.Connect\CurVer]@="ACT.Connect.1"
[HKEY_LOCAL_MACHINE\Software\Classes\ACT.Connect.1]@=""
[HKEY_LOCAL_MACHINE\Software\Classes\ACT.Connect.1\CLSID]@="{4899F9F9-3960-4768-B17E-09AC400164A5}"
[HKEY_LOCAL_MACHINE\Software\Classes\CLSID]
[HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{4899F9F9-3960-4768-B17E-09AC400164A5}]
[HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{4899F9F9-3960-4768-B17E-09AC400164A5}\InprocServer32]@="\"C:\\PROGRA~1\\MICROS~4\\MICROS~1\\act.dll\"""ThreadingModel"="Apartment"
[HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{4899F9F9-3960-4768-B17E-09AC400164A5}\ProgID]@="ACT.Connect.1"
[HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{4899F9F9-3960-4768-B17E-09AC400164A5}\VersionIndependentProgID]@="ACT.Connect"
[HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Word\Addins\ACT.Connect]"FriendlyName"="International Character Toolbar""Description"="Insert characters from different language alphabets into your Office documents.""LoadBehavior"=dword:00000003"CommandLineSafe"=dword:00000001