Nope, that would screw your boot file. Also, the windows folder is on the C:\.
Personally, I make my system partition smaller and then store everything on a larger partition on the same disk.
And like E said, using software to do this is very risky.
If nothing else and you are using windows XP (I think 2000 can do it too). Convert C to ntfs and then convert both c and d to dynamic disks. Then just resize C:. All of this can be done with in Windows without special software. But once you go to dynamic disks, you can't go back without a full format and you can't install Linux or anything like that.