Taking the HDD out and reusing it in a new PC is leagal as long as you only have one live PC with that code etc.
I've just got a new XP disk of MS for £17 as the HDD in a laptop had died and I was going to get a new HD for it and re-load. The vendor, (tiny), had gone bust a couple of years ago and hence MS were willing to send me a Cd-Rom on payment of the distribution costs.
If the vendor / maker is still going they should to be able to do the same for you, basically by verifying your OEM Certificate of Aunthenticity and license number etc. (The little holograpghic sticker on the base of the unit).
NB You have to contact Microsoft Direct Services to be able to go down the MS route, contact details below:
Good day M, Thank you for your interest in our program. Please use the following link for placing your order for the Windows XP Home media:
If you have any further questions please get in touch with us and we will be happy to assist you in any way we can. Kind regards Steve Granger Microsoft OEM/SBC TeamCSDSBC@msdirectservices.comPhone
: 0870 60 10 100Fax: 0800 03 24 485