You can still reactivate your OEM installation on a replacement motherboard in the old machine. For instance, if your XP machine had only been 6 months old, and the motherboard failed, you could have replaced the motherboard with a similar model, but six years on, the availability of boards and processors has changed. There is no time limitation on the license.
It does not mean that you have to throw away your old XP - you may need to reinstall XP to accommodate the new hardware, but you are within your rights to do so. Whether your OEM left you with the means to reinstall - disks, or a recovery partition is a different matter.
However, a dual boot is probably not going to be legitimate.
What the Microsoft Windows Activation Technology and Microsoft Genuine Advantage programs are designed to prevent is not people continuing to use their old operating systems (even though they have ceased to be profitable to MS), but to stop people distributing a single copy of the OS on several different machines, either for distribution or within a home or business environment. People with one wooden leg, eye patches and parrots on their shoulders, for instance.
If you do reinstate your old hard disk on a new motherboard etc, a live telephone reactivation will be required, and your reactivation details will be recorded by the Microsoft operative. http://answers.microsoft.com/en-us/w...2-909118622476