Shwing Text in Category Post

Hi

I am using twenty ten theme. I want when I open my particular category and a particular Post under that category i.e Title “Great People” should show a particular image. I show 10 post at a time in category. So how to add some condition in loop.php or somewhere else. I am unable to point that particular post of category post. SO where to use the conditional tag and what php code or conditional tag to be used for it.

Thanks experts