Well, I jumped right in the middle of season three and then went back and watched things later so... you might want to read up a little first? I know that they're doing a "What the Frak is going on in BSG?" eight minute recap during some terrible monster movie today, I'm sure it'll get leaked to the internets. XD You'll miss out on what's going on with the side-plots, but the main plot is pretty easy to get into--it's just survivalist sci-fi with random religious insertions.

This Fan Wiki is pretty much the best source outside of watching episodes. (http://en.battlestarwiki.org/wiki/Main_Page) I use it all the time to make sure I know what's going on when I miss stuff. XD

~Cendri