The Loop question

Hello guys, I’m new here. I’m exploring the Codex looking for tips to aply my template, and I’m stuck.

My problem: I’m editing the category.php template file. I have a number of categories and I want them to apear in a certain way.

The only problem is that I want to style the first post of this page in a different way than the other posts. I don’t want to exclude a post by ID or something, I’m only looking for a way to ad some div, automaticaly, to the first post, so I can give it a different style.

Can anyone of you help? I’m trying, unluckly, to use Query, but when I do that my Category page shows all my posts, of every category, and I only whant to aply that to the current category of the opened page.

If anyone can help, thank you. xD