SATA II was actually the organization's name back when SATA was being redesigned, which led to some confusion. The organization is now named SATA-IO short for Serial ATA International Organization.
What most people and websites listing specifications call "SATA II" is most often SATA 3.0Gb/s or SATA/300 as opposed to the original SATA design which we call SATA 1.5Gb/s or SATA/150.
The more advanced SATA/300 is backward compatible with SATA/150, so what you want is a motherboard that supports SATA/300 (again sometimes referred to as SATA II, but check to make sure) and your hard drive itself too would optimally be SATA/300, but SATA/150 is fine. Burst speed will be lower with SATA/150 hard drives, but the sustained rate will be the same because current hard drive technology at the current standard consumer speeds don't surpass SATA/150's upper limit (but the burst speeds can).