velocity - Convert orbital elements to positions and velocities

I wrote a similar N-body orbital program a few years ago.
To obtain the initial velocities and positions for Solar System bodies I used a free program called PLANEPH.
Download available at:- ftp://cdsarc.u-strasbg.fr/pub/cats/VI/87/

It can give you 3D xyz position and velocity of solar system bodies at a particular point in time with resolution of a few seconds of time as I remember.

The user interface is a bit old-fashioned (DOS-style) but it seems to work OK. I ran it on Windows 2000.

I used PLANEPH to extract Heliocentric Coordinates then I had to convert to Solar System Barycentre frame using data on planetary masses obtainable elsewhere (e.g. NASA).