Hard Drive Copy

I am currently in the process of building a new computer. My old computer has a 6gig HD currenly in it with Windows XP SP2 installed on it. What I would like to do is possibly install the 6gig HD into the new system as well so I will already have XP loaded onto it. I was told by someone that this would not be possible as it would not recognize the new hardware and therefore not boot Windows. Is there any way around this at all? Or is there a better way to go about doing this so that I will still be able to use the Windows XP that I have already. I do not have my registration code anymore as it was installed by a friend who works in IT and had a copy laying around. Thank you in advance for your help.

You can try by removing all the hardware drivers from device manager then shutting down and moving the hard drive over.