Hello,
CorelDRAW Graphics Suite 12 has not been tested on Vista by Corel and is not supported. Corel only started supporting Windows Vista with CorelDRAW Graphics Suite X3 Service Pack 2. There seems to be some mixed results in using version 12 on Vista. Here is a thread on CorelDRAW.com that you might find interesting. You can search through previous posts for more information.
Gérard