The download is available on connect.microsoft.com.  You'll have to get a "liveID" using your email address, if you haven't gotten that already.  The download process has 3 steps:

  • 1. Search for windows HPC under CONNECTION DIRECTORY, SERVER, then HPC (at the bottom of the page).
  • 2. Apply to the "Beta" program by filling out a 13 question survey.  You instantly get access to download RC1 after that.
  • 3. Download the product, which is about 350MB or so.

The entire process took me about 10 minutes not including the download time.  The Getting started guide included in the HPC Pack is a step by step guide for installation and node deployment.  Of course, you will have to have windows 2008 server to run the HPC pack. The server standard trial can be downloaded from this link.