SATA II is a newer version of the SATA standard that incorporates faster bus speeds over SATA I. Whereas SATA I runs at 150MB/s SATA II runs at 300MB/s. The specifications that govern the design of SATA II ensure that it is backward compatible with SATA I.
This means that the drives will work, but will only transfer data at half the designed transfer speed (buffer to host).