Getting and Installing Zotero
Zotero will run on any operating system. Installation only takes a few seconds.
Open http://www.zotero.org/ and click the red "Download Now" button. You have a choice to download the current version for Firefox, OR choose the standalone and a browser connector for that. If you download the Firefox plugin, you need to restart Firefox and you're all set! You'll see a small Zotero button at the bottom of your Firefox window.
If you choose the Firefox version, you'll probably also want to download and install the Microsoft Word citation plugin or the OpenOffice plugin. These allow you to easily cite items from your Zotero library in your papers.
If you choose the Standalone version, you'll want to download the plugin for Google Chrome or Safari or Firefox.
Problems installing? Check the Zotero installation page.