to enable X11 forwarding from nokia 770, needs:
first, your ssh daemon should support X11 forwarding, as I know, the openssh-server provided by the repository of maemo2.x doesn't support X11 forwarding, but dropbear works.
and a "real" xterm, I don't think osso-xterm supports X11 forwarding, to make xterm you need build x11proto-core-dev, libxmu, libxaw first.