i think I'm stupid, how do I make a custom "if condition?"

[lackhand]

Since purchasing vBulletin a few weeks ago, I have had a pretty easy time customizing templates to my liking. I am however finding it difficult to use a custom "if condition."

The change I am trying is for vBulletin Blog for my blog with my custom style.

What I would like would be to have a picture be auto inserted below the blog entry title according to if it is in a certain category. For example, if the entry was in the "pizza" category, a picture of a pizza would be auto inserted under the blog entry title.

I would know how to do this if the $show[pizzapicture] already existed in the includes, but I have no idea how to create it. I figured it's in a .php file, but not sure.

Thanks in advance and thanks for all the template articles that helped me design the look of my forums.