As promised, here are the details:
http://blogs.microsoft.co.il/blogs/danielp/archive/2008/01/29/temporarily-bypass-windows-server-2008-and-windows-vista-activation.aspx
So easy it's amazing no-one has thought of it before... Read the article and enjoy.
Disclaimer: This article is not intended to be used as a hack/crack or as a way to bypass the legal activation process required by the EULA. The only reason for this article is to help those of you that are stuck, like I was, without the ability to activate their legally owned copy of Windows because of some wrong configuration setting. This article is not a hacking guide, nor is it to be used as an encouragement to use your operating system in ways that are not covered by the EULA. You should only use legally bought copies of Windows (or of any software for that matter). What you do with this information is not my business, and I cannot be held responsible for any legal results that may occur if you so chose to follow the steps outlined here. To make myself absolutely clear – Buy a legal license, activate your copy of Windows, and always use a legally owned product ID.