The hard drives do not care whether they have Vista, data files, music, etc. - In order to transfer one drive from one computer to another, make sure that the drives are compatible; either IDE to IDE or SATA to SATA. IDE hard drives will not fit SATA connectors and vice versa. This information regarding IDE or SATA in your computer will be displayed in your computer specs. - And, the manual will clearly explain which drive is the main OS drive, the capacity, and which drive is the auxiliary drive.
After you save all the files on the drive that you are transferring, it is best to format it NTFS, and then install it into the new computer.