Step 7 Lite is free, but I've never heard of a free version of PLCSIM, the simulation software for S7.
Step 7 Lite can be downloaded
here on the Siemens site. Don't forget to register for free.
As for the simulation, depending on the use you'll make of it, your local Siemens rep might help you out (although I doubt it). Just ask, "no" you have "yes" you might get.
Kind regards,