Hi there, I'm trying to transfer album.php from the template directory to another one (external but in the same site). What do I have to change in order to make it works?

Why would you want to do that? Zenphoto themes do of course not work if not present in the theme directory... Either you need to better explain what you want to do or you have a great missunderstanding of how CMS work and need to learn a few basics first...

I've got a website with a "gallery section". I just want to separate zenphoto-admin folders and the template. So this will be the structure:

root/admin/zenphoto
root/(site content)

in site content i need to create a page with the gallery that will be the "album.php" page

I still don't understand what you want to separate and why... You can't change the structure of Zenphoto.... Themes and the admin are separete. The core and the admin is with "zp-core" and the themes are within "themes". If you want to have a gallery section on your site why don't you just place a link to the Zenphoto install in the main navigation? No one will care where that actually is...

"No one will care where that actually is..."

I just want to avoid this infact... so you've well understood

If you want Zenphoto in another place you have to move the full folder of the installation of Zenphoto to that place. You can't take individual files and place them elsewhere, with no CMS out there.