Oracle Application Server 10g Release 2 (10.1.2.0.2)
If you want to install just Discoverer Plus and Viewer, and do not want to associate it with an infrastructure, you should use the Business Intellence option (shown below). This also has a smaller download footprint - 1GB.
If you want to use Discoverer portlets, public connections, SSO, etc... then the full installable is what you need:
The Windows version is not yet available, but should be out soon enough (don't have dates yet).