voting with sessions

hi - i want to enable voting on my site, but i don't want to require a
login. i realize people might clear their cookies and revote, that's
fine for now. the questions are:

1) how should i do this? Do i grab the id from the sessions table
and link it with votes, or do i store the session hash in the votes
table directly?

2) How do i ensure the session doesn't expire for a long time?

3) how do i get the 'session' itself in rails? i.e. what does the code
look like?

4) when does the inital session begin? when the user firsts vists my
site? or, do i configure this?