Not sure about the Itunes issues, not had anyone ask about it yet so am assuming it can be transplanted without a problem, maybe a visit to their website FAQ might reveal more though I have found the site to be high on adverts and low on info in the past.
As to XP, to date I have had no problems at all tossing one of my hard drives loaded with XP Pro and a full range of generic drivers and diagnostic software into any machine I come across without the dreaded reactivation thingy coming up once, however this involves only plugging it in, the times I have had to reload XP it has always demanded reactivation and of course the key has long since expired and I have had to rely on the automated system which has always given out a new key along with instructions on how to install same, Process takes an age to complete though but does work and the only time any explanation has been asked for a simple HDD replacement answer returned the desired response.