Installing SharePoint Designer 2013 Issue: You must uninstall office pro plus first....

I came across this issue a while back while setting up a new development environment, i had installed VS2012, Office 2013 and was trying to install SPD 2013, I ran the setup and during the preflight checks it failed with the following message:

Why? why on earth must I un-install office to install SPD?, well as it turns out Office 2013 added a registry key(typical...) that the preflight checks, this key looks as though its not needed but is still added, possibly something that was meant to be deleted but wasn't.

So to fix it!:

Open regedit.exe (Run -> regedit -> Enter)

Find and delete the following key: HKEY_CLASSES_ROOT\Installer\Products\00005102110000000100000000F01FEC 

Note: if you can't find the above key, just find the key with prefix: 00005102, and suffix: F01FEC, and delete it. (Before deleting it, backup this key by exporting it, never a good idea to mess with the registry before backing up the original state).

Now that that's gone, try the installer again, hopefully it should now let you install SPD unhindered!