Don't think that really addresses the question here Count.
Personally I would leave the C partition well alone unless there is a real pressing need to resize it, resizing a system partition always carries a risk and it's not something I'd do unless absolutely necessary.
Either install it onto D as it is, or resize D and install it onto a smaller 3rd partition if you want, neither of these risk anything on the C drive.
(or if you just want to play with linux and your machine is a reasonable speed then install it as a virtual machine under windows)