Is your XP installation XP pro or XP Home? Is the ex Vista SATA disk configured as a basic volume or as dynamic?
XP Home cannot import a foreign disk if it is configured as a dynamic volume - XP Pro should be able to do so. "Import a foreign disk" is an option that you should get if you right click on the disk in disk manager.
Since the disk is good, you should be able to read it if you do an XP repair install but you have also to prepare a floppy disk with the SATA drivers on it and press F6 early in the XP install routine to load the additional drivers from the floppy.
Google "XP cannot see SATA drive" and " XP import foreign disks".