Comment 1 for bug 63412

By digging through the source, I have found the following array at line 54 of connect.c.
  gchar *size_items[] = {
    _("640 x 480 pixels"),
    _("800 x 600 pixels"),
    _("1024 x 768 pixels"),
    _("1152 x 864 pixels"),
    _("1280 x 960 pixels"),
    _("1400 x 1050 pixels"),
          NULL
  };
So it appears that the resolutions are hard-coded and static.

Moreover, I have looked through some of rdesktop's source code. It looks like it will be happy with any resolution given to it for window geometry (but I have not tested this in practice). I would suspect VNC is the same way.