As I mentioned in my original posting, I can do exactly the same (F8->menu->"send Ct-Al-De") with my client (xvnc4viewer) when the server (WinVNC) is running on Windows. Alas, this doesn't work with the same client and the server (x11vnc) running in a TDE session.
Does it work when you run FVWM or TWM instead of TDE?
Nik