You cannot buy legal versions of Windows at discounted prices, it just does not happen. If it is a genuine 100% legal and legitimate version of Windows, the price difference won't be much more than a few dollars, ANYWHERE. That is the long and short of it. 1/3 full price? Its not a genuine or legit copy, you can bank on it. But to that end, just because you buy it now, does not mean you have to install now. You can buy it, save it, and install it anytime you choose. Again, if it is a legal version. Once you install it though, if its an OEM verison, you cannot move it to another computer. The license is only good for a install onto 1 PC. If it is a full retail version, you can install again on another computer, as long as you remove the first installation. Moving a drive with a OS installation from 1 PC to another technically can be done if both PC's are very similar in hardware. The more different they are the more likely it will not work. Its always best to do a fresh install, rather than try to move a drive with an installed version of Windows on it.