I searched for a compatible partition manager for Windows Vista and I was surprised to find out that even the latest version of Partition Magic is not Vista Compatible.

I began searching for an alternative and I found it: Paragon Partition Manager 8.5.

I used the software to transfer free space from one partition to another (D to C, where my Vista instalation is located) and it worked perfect. A reboot was needed to apply the changes.

Hope it will do the job for you as well.