How to make a poster

Yesterday, I was trying to figure out how to enlarge a section of our Alphabet Fair unit so that I could have a large classroom poster. First I tried going to a copy store, but the starting cost to print one poster sized image was 25 dollars. Then I found this site that will take an image and divide it up so that you can print a poster sized image on your regular printer. I imagine I'll be using it a lot this summer as I prepare for next year.