There are many ways to get OpenACS working for you quickly and/or easily. See Try OpenACS for demonstrations, automated installations and hosting solutions.
These are the steps involved in setting up OpenACS. Before beginning, read about ways of getting help (en:docs-admin-help) during installation. Also, read the documentation completely before beginning, to minimize the chance of any surprises during installation.
These pages contain notes where installing OpenACS on a specific OS different from the *nix standard installation instructions (above). These notes also refer to helper scripts and automated installers that can really simplify installation: