How can I determine launch windows to different planets from different planets?

[Kerbface]

I'm writing something that involves interplanetary missions possibly involving more than just Earth-to[planet]. How can I determine launch windows from other planets, like Mars and match them to dates in the future? Usually if I look up launch windows to a planet, I can only get Earth launch windows, which makes sense unless you're writing certain science fiction stories. Also, I usually only find the periods, but not actual dates (even one from which I can calculate the dates myself).

Edited June 1, 2013 by Kerbface

[Poldarias]

Well im sure the planet has to be at a certain position, but im not sure how they calculate it. if you want to find out best looking for probes sent to that planet then look at what degree they are relative to earth, use a simulation like NASAS EYES and look to see when it happens again. Im sure there's a way to find out somewhere on the internet what is a lot easier though.

[Pyotor Gagarin]

The Maths in Kosmo-not's Interplanetary How-To Guide are applicable for orbit to orbit transitions in general.

The masses and orbital radii of the planets should be pretty easy to find on the internets. Hope that helps!