You shouldn't have any problems with Novatech, I have bought a Desktop and a laptop from them and also bought the O/S seperately. I always like to do this so as I have the full Windows CD at all time. Not a backup partition on the HDD.
Make sure the laptop and the OS are compatable for their drivers, or you could be in for trouble? Go for the laptop make and the OS from the same supplier, or make sure the OS will install on it? David