Adding art to categories

[Moderator note: Topic title de-capped. Please do not shout at us.]

My blog is http://www.sammaronie.com. I have a couple of categories on my menu, one in particular is called Exclusives!.

I have a masthead that i’d like to import there so it appears when i post something. How can i do this? Remember—you are dealing with a challenge person here! lol. Thanks!