Anyone that’s worked with SharePoint 2007 or WSS 3.0 and SharePoint Designer, and is moving to SharePoint 2010 might be a little confused about how to get the new Designer client. Previously, it was (and still is) delivered through MSDN, but after the announcement that it was made free of charge, it was made available for general download.
SharePoint Designer 2010 is ONLY available through public download. You can find the home page for the product here, and download links for both 32 bit and 64 bit are at the bottom of the page.
There are a few important usage notes here. Firstly, SharePoint Designer 2010 works ONLY with SharePoint 2010 sites (not 2007 sites). Designer 2007 works only with 2007 sites, and not at all with 2010. Therefore, if you find yourself like I do in a situation where you need to support both environments, you’ll need to keep both installed side by side.
This however brings up another issue. The bit level of all Office applications need to be the same. SharePoint Designer is an Office application, and Designer 2007 only had a 32 bit version. In this scenario, you are restricted to the 32 bit version of Office 2010. In truth,this isn’t much of a restriction,and Microsoft itself suggests that you use the 32 bit version of office unless you have a compelling need for 64 bit. The 32 bit version is more compatible with add-ins, etc.