Image galleries and attachment.php

I’m having a hard time figuring out how images work. Basically I’m making a photoblog, so each post will have a bunch of photos. The way we have it laid out, there’s a big image at the top of the page and a series of thumbs under it. Pretty standard. The upload side is all working as it should but I can’t figure out how to control the output — using the shortcode I seem to have little control over how much space is around each thumbnail, for example.

So, how can I select the first image in a gallery and use it’s large image instead of it’s thumbnail? How can I bypass the inline css? How can I play with the links, so I can add a lightbox-style interface?

Thanks a bunch.