Upload & Sell: On
I suggest you get a copy of John Harrington's book "Best Business Practices for Photographers" It contains lots of info on how licensing and contracts work for photographers as well as samples.
What you want to do is to license the photos to the company for a certain number of printing or certain number of calendars. And for a limited length of time (like one year only).
Keep in mind that they will want as much as they can get for as little as they can spend, so you have to get some education before you get taken advantage of.