I tweeted about this yesterday when the bits actually appeared, but here are the URLs from SharePoint MVP Sean Wallbridge:
SharePoint 2010 is on MSDN.
Microsoft SharePoint Designer 2010 (32 bit)
Microsoft SharePoint Designer 2010 (64 bit)
Reminder: SharePoint Designer 2010 only connects to SharePoint 2010 sites. You will want to continue to use SharePoint Designer 2007 to connect to your WSS/MOSS sites.
Also note that you can't mix 32bit and 64bit Office versions, so you’ll want to download either Office 32bit and SPD 32bit or the 64bit versions of both.
Also, you might want to read the SharePoint 2010 hardware and software requirements
- a shout out to the MCMS folks