In about 2002, I bought a new computer because I wanted one which ran XP. It was worthwile upgrading to XP from windoze 98 because of the photograph handling facilities which the new O.S. offered. The computer, made by Maxdata came with an XP rescue disc.
About two years ago, the copy of XP needed rescuing and the disk did exactly what it said on the label. About nine months ago, for various reasons I decided to upgrade to a system with a dual core processor. I bought all the bits I needed and put one of the DVD ROM drives from my old machine in (which I had added - it was not original equipment) as this was the one item I did not need to acquire new. All bits were plugged together and on switch-on (much to my suprise), I was merely asked to put a bootable disc in drive D:. In went the rescue disc from my old machine, and after formatting the new hard drive, XP (without even Service pack 2) was installed. As my old machine had been dismantled and would never be used again, I felt justified in doing this.
Naturally I was asked to validate my new copy of XP. I had read somewhere (probably here) that the way to do this is to use the "validation by telephone" service. I indicated that I lived in the U.K. and was given a freephone number to ring. I did so and entered the validation code given by XP on its validation screen. I was told this was not acceptable and instructed to push the "code generation" button. I did this and was asked for the serial number on the label attached to the computer case. My old case was handy so this was entered and a new validation code generated. On entering this via the freephone number, my copy of XP was declared valid and an appropriate validation code was given. The XP serial number label is now attached to the case of my new computer.
A few months later, my wife's computer needed its copy of XP reinstalling. I used the same XP rescue disc as her machine was never supplied with one. I went through the same excercise except that when the first code generated by the newly installed copy of windoze was entered the telephone validation service advised me that the copy of XP was invalid and I must contact a certain website to validate (i.e.) pay Microshaft. This was despite the copy being run on a totally kosher computer! I though about it and pressed the code generation button on the validation screen despite not being instructed to do so this time. Once again the serial number was requested which was obtained from the label on the case, a new code was then generated and the telephone promptly validated this copy of XP!
IMHO, provided you have a unique Windoze serial number which is not being used on any other computer then you should be able to validate the copy of XP which is running on your new machine. Regrettably, under certain circumstances, the licensing of XP can be a grey area on a new machine, but if you have a copy which came with a computer you have acquired, you have a license to use it on one machine for ever. Why you shouldn't be able to transfer it to another machine, I really don't know provided it is no longer used on the original machine.
After all, Microshaft have a new shiny operating system to enforce its complex regulations on now so why they need to be so keen with XP these days I really don't know.
P.P.