I've done this before in Photoshop a few years back when I have to decorate our class board, but i've forgotten how.

What you're looking for Panaromic Image Printing, refer to this site for more information.
http://www.panoguide.com/howto/display/printing.jsp

Although no photoshop tricks there, they suggests alternative software like cPicture or PanoPrinter. Worth a try and see if it helps!