You need to change the RAID controller card's driver from Vista's to the one included on the Adaptec driver CD (Adaptec Installation CD). The driver CD was included in your system's toolbox.
1. Find the RAID controller in Device Manager and choose Update Driver Software.
2. Browse My Computer.
3. Choose "Let me pick from a list of device drivers on my computer."
4. Choose "Have Disk / Browse".
5. Point to the "CD:\windows-win2003\driver\amd64\" directory.
6. Once the driver is installed you should see an option for GPT in Disk Management.