can you symlink or mount the temp dir in any way to D:\ ? i suppose not, from what i remember.
what i would probably do is tarball the windows partition, then unzip the tarball onto d:\ then i would use fdisk or cfdisk to hide C:\ from windows (perhaps even reformat it as ext2?) so that your previous d:\ was the new c:\ and go from there, now you have enough room on C:\ and your iso will end up in the right partition that you were aiming for in the first place.
actually i just noticed that you have c: and d: on different physical drives, why not just tarball c:\ then untar it onto d: and then swap the drives round so that hdb is now hda and vice versa? then d: will be c: and vice versa too.
any good?