Disclaimer: I know the original post is old but I'm still using my SK-8845 keyboard and thought this might help someone else.
Lenovo stopped updating the drivers for the SK-8845 keyboard a long time ago. So, I checked out their site for a similar keyboard and found the 55Y9003. I downloaded and installed the drivers on my Windows 7 HP laptop and my ultranav keyboard functions flawlessly. The function Standby/Hibernate key even puts my laptop to sleep.
I have a couple of these and why Lenovo sadly removed the USB ports from the newer models which I use to connect to a small LED USB lamp to light the keyboard is beyond me (probably to reduce the costs...)
Those ports makes using it a breeze in darkened room.