split photoshop image over several pages

I haven't done any that are bigger than two sheets of transperancy, but what I did was make the width of my image 11 inches since that is as wide as the transperancy can be. I made the height as big as I needed it to be. Then I created my image to fit that width. Then cropped the image to 8.5x11, and made sure to make the 11 inches go from one side to the other. I cropped it on the top of the image the first time, saved that file, then undid that crop and cropped again using the bottom part of the image the 2nd time. The middle part of the image ends up on both prints so you can line them up.

This may be clear as mud.

You could set it up manually by cutting out pieces with your select tool set to whatever the maximum size of your printer's output (8.5x11 minus margins), but I could have sworn there used to be some software that would automatically do this, taking into account your printer's margins, etc. I was never fond of Publisher's method of doing it with registration marks that eat up your maximum print area.

Google rasterbator
Illustrator also allows you to tile a print over several pages.
Hope it helps.