If you missed the pre-order price of £49.99 for Windows 7 then this isn't a bad alternative?
Argos are again offering 20% off pre orders using the code GAME20 bringing the price from £79.99 to £63.99
They also have a two £5 vouchers for orders over £50 so thats it at £53.99
Finally use Quidco to get 1.5% cash back so down to £53.18
Oh and free delivery as well.