Based on the fact that Windows 8 is terrible to use (I have used many builds now), and you won't be able to buy a full retail version of it anyways, you might as well just go for Windows 7 now. Windows 7 is a nice, easy to use operating system and using 8 will only lower your opinion of Windows (
imho). They have basically just placed the Xbox Dashboard over the interface and force you to use it - there isn't even a sodding desktop anymore =[ - the Windows key will open the silly guide - you can't tell I don't like Windows 8 at all can you XD
tl;dr Buy Windows 7 now!