As an owner of two N800s, but no N810s, I can't answer. Anyone?

(perhaps you should try running "xmodmap /home/user/.Xmodmap-keymap" first?)

The Maemo VNC Viewer works great; unless you want something specific from the xtightvncviewer that the Maemo one doesn't provide (I can't imagine what that would be), I would recommend just using the Maemo one.