Next/previous links using excerpt on main/category template

I am building a photography portfolio using wordpress as the back end, I have one post per page and would like to make links to the next/previous page on the index/category templates. I want to use the next/previous posts excerpt as the link.

I am currently using, <?php next_posts_link() ?>, to produce the link for next/previous. And custom fields on each post to add the thumbnail, excerpt, to the next/previous page. Which works fine right now, albeit very tedious, but I’m also adding tags so the custom fields on the tags page, index.php, link back to the next/previous page on the category template.

Is there any way to produce the links I described? I would like to do this in template rather than adding more custom fields, as is becomes very tedious work when adding them to a hundred plus posts? Did any of that make any sense?

Josh.