For those who are interested there has been the following posting on one of Xfree.org mailists from Alan Coopersmith of Sun X-window engineering giving some very helpful information; He says:
You might want to look at GOK - the GNOME Onscreen Keyboard, which while it
was developed for accessibility uses, has also been put to good use in other
environments, such as touchscreens, and has been used with gdm to provide a
login screen.
http://www.gok.ca/