AFAIK, Vim isn't able to tell what screen resolution you're using.
I did notice that my version of gvim running here on
Debian/Testing that gvim *somewhat* respects the usual X
-geom parameter. It seems that it handles the size
correctly, and positive positioning, but it seems to ignore
the leading minus if passed in such as
gvim -geometry 80x50-0+0
which, with other X applications, would create the window
and have it slammed against the right edge of the screen
("-0"). I don't know if this was what the OP was trying to
do (position the window either along the right side of the
screen, or some fixed offset from the right edge of the
screen), but properly respecting this standard X setting
would be quite helpful.
bash$ man X
(searches for /^GEOMETRY)
-XOFF The right edge of the window is to be
placed XOFF pixels in from the right edge of
the screen. XOFF may be negative, in
which case the window's right edge will be
off the screen.
Just a little bug?
-tim