On 30 Oct 2004 18:07:07 GMT, Laurens Rossi
wrote:

What I'm interested in, is the motion of the sun itself related to the
position and motion of the planets.

The sun moves about the center of gravity of the solar system, the
barycenter, which is roughly 1/1000th of way between the Sun and
Jupiter. Steve Moshier is kind enough to provide a program that
computes positions using numerical integration (that is, using
gravity): http://www.moshier.net/ssystem.html.