The OCZ Vertex 2 will definitely work when connected to a SATA III (6 Gb/s) port on your motherboard. SATA III (6 Gb/s) ports are backward compatible with SATA II (3 Gb/s) devices. The SATA III port will simply function as if it were a SATA II port. No problem.
Sometimes SATA data cables are advertised as being either SATA II (3 Gb/s) or SATA III (6 Gb/s). They are identical. It's just an advertising gimmick.