If your install disk has "10.5" printed on it, (lower left side of the disk), then it shipped with the original (10.5.0) version of Leopard. Subsequent install disks are labeled 10.5.3, etc with the minor version. AFAIK, this is true for all of 10.6.x back through at least 10.4.x (I don't have any pre 10.4 disks nearby to check)