The server is setup as pure Nginx, therefore mod_rewrite doesn't exist.
Except from that it should work. Nginx doesn't read the .htaccess file so the only thing that should be needed as a replacement are rewrites for nginx.
The software is installed on the root directory as set up.
I've transfered all the files multiple times to see if it would do any difference.'
From the log:
2012/12/24 15:40:43 [error] 20141#0: *7 open() "/opt/nginx/html/ci/install/requirements" failed (2: No such file or directory), client: 31.11.140.236, server: domain.se, request: "GET /install/requirements HTTP/1.0", host: "domain.se", referrer: "domain.se/install/requirements"