*NEW* Version 2.0 of DDRMenu, which is the default menu provider in DotNetNuke 6.0, is now available for download on CodePlex.
If you still want version 1, download the package according to your version of DotNetNuke:
(Save the package rather than opening it, you'll need to upload the ZIP to your server when you install it).
Be sure to sign up for updates (choose one from the list at the side of the page) to be notified of new templates, performance improvements and maybe even the occasional bug fix.
You should probably take a quick glance at the installation instructions and the getting started guides as well.