Error 0x80070643 Service pack 1 install failure

You could point both to the D: drive, but they must go to separate destinations.
- so just take the default location and change the drive letter
Note that it's generally recommened NOT to take this approach, but to set up a file structure on the second drive and individually point installers at the folder when possible, since some programs will be hard-coded to the normal location and Windows may not see them there.
Except where space is very limited, there's no advantage to placing the Program files folders on another partition/drive anyhow.

My Windows partition currently uses 106 GB - and that's with a huge number of programs installed (Including things like Office, and a couple of very large applications (one of which takes up 4.5 GB in its own root folder!).
The Windows folder itself is around 30GB, and the Program Files folders take less than 20GB.
One space-hog is actually the ProgramData folder - 6GB here.
The Hibernation and PageFile files alone take up over 12 GB.
I move my 'Documents' folder out to a different parttition - but the residuals in the C:\Users heirarchy still manage to gobble almost 15GB.

Installing programs using the custom installation methods will inform Windows sufficiently of their type for it to be able to work out which is what in terms of bitness - As far as I know, unless you install programs with different 64-bit and 32-bit versions, you can install them all to the same folder, and Windows will take care of the rest.