If you can't find the settings, there is the solution of changing registry keys. Here is the text file for the registry entries, just edit the fields (you can change the icon, the path to bitmaps, the default IM, ...; be careful with registry edition, use it at your own risk ...):
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Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}]
@="Happy Tapping Keyboard"
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}]
"BitmapFilePortrait"="\\windows\\ip_AC_QVGA_P.bmp"
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}]
"BitmapFileLandscape"="\\windows\\ip_AC_QVGA_L.bmp"
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}\DefaultIcon]
@="\\windows\\ThumbKeyboard.dll,0"
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}\IsSIPInputMethod]
@="1"
[HKEY_CLASSES_ROOT\CLSID\{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}\InprocServer32]
@="\\windows\\ThumbKeyboard.dll"
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You can add the following lines to force the default IM, but the device input may got locked. It is preferable not to use this and try to choose your keyboard with the normal selector or the one given (for WM5)
[HKEY_CURRENT_USER\ControlPanel\SIP]
"DefaultIM"="{F9A103FF-B5E2-4eae-8C34-0ADC26116C4B}"