SCSI is a type of interface used for communication between the Motherboard and other devices. There are different types of SCSI, such as Fast SCSI, Fast-Wide SCSI, Ultra SCSI, Ultra-Wide SCSI, Ultra-320, Ultra-640, etc etc. You need to find out what kind of scsi you need. To make your computer support SCSI, you will need to purchase a SCSI Adapter card. You can purchase this online or even places like Best Buy or CompUSA. 90% of the time, Vista should recognize the adapater and automatically install the necessary drivers. You can learn more about SCSI at:
SCSI - Wikipedia, the free encyclopedia