multiple templates for a single theme

Hi. I’m trying to develop a site whereby each category will have a customized header. In other words, if you read a page for Category A, it will show Header A; a page for Category B will show Header B, and so on. I realize that this will require a different header page for each category, but how to I write the PHP so that it will read the correct header file for each category? I should point out that I am not a PHP programmer.