Here's an extract from the Windows 7 Home Premium EULA :-
"By using the software, you accept these terms. If you do not accept them, do not use the software. Instead, contact the manufacturer or installer to determine its return policy. You must comply with that policy, which might limit your rights or require you to return the entire system on which the software is installed.
As described below, using the software also operates as your consent to the transmission of certain computer information during activation, validation and for Internet-based services."We are given the option not to use Windows on our new PCs, but we have to contact the manufacturer to determine its return policy. If we want a refund for the cost of Windows this is obviously a necessary step, as Microsoft do not offer refunds directly. Recent cases in the EU have demonstrated that the refund policy of some manufacturers involves returning the computer to them for Windows to be removed. The EULA seems to leave open the possibility that you will only be able to get a refund for the whole system and be left needing to buy another one.