Trying to install the 32 bit version of SharePoint Designer, or the 64 bit version, resulted in a dialog error message saying;

The installation of this package failed.

With nothing in the event log shedding any light I tried re-downloading the installers, with the same result.

My environment was Windows Server 2008 R2 x64 Standard + Domain Server, with SharePoint 2010 Enterprise and Office 2010 x86 installed.

Googling turned up nothing useful, so for no apparently good reason I decided to check the digital signatures of the downloaded files, which surprisingly showed they weren’t valid.

Re-downloading the files (yet again) on a different machine, was more successful and showed the digital signatures to be valid.

Attempting to install now, proved much more successful.