You should use the currently available form. For non-calendar years, you write in your fiscal year on the dotted lines right under the "Corporate Tax Return" caption. If your fiscal year starts in 2012 and ends in 2013, you should be using the 2012-year version of the form.
If its the first time you're filling the form 1120, I'd suggest talking to a professional (EA/CPA/Attorney/Tax Preparer) licensed in your state.
In fact, I suggest always to have a professional work on your corporate tax returns.