Actually I have just re-read Saab's post, as far as I can see I am happy with that, I did build this system myself, ok I moved the HD from the original machine that was bought from PC World with windows pre-installed, I cant remember how I did it, but I registered again over the phone and it worked...for a good two years, now I want to re-install, the restore disks don't work, probably because it is no longer the original machine, fine, no problem, so all I want to know is, when I stick the new disk in, will it allow a fresh copy to be installed over the existing one, therefore cleaning the HD and having a fresh install, I suspect that I will only find this out on trying it.
If not that was an expensive mistake, to be honest the sites are not exactly clear on what OEM's are, you just type in Windows XP Home and it gives you that option.