Minymigitover9000 :
By clean you mean a new copy of windows xp being downloaded, right? If so then no the old hard drive already had windows xp
A Clean Installation is one done after the Hard Drive is formatted.
An installation over an existing Windows XP is called a Repair Installation.
What you apparently did was just add the old hard drive with Windows XP to the new computer... and that is what causes the blue screen... The Windows XP on the hard drive has drivers for the old motherboard installed which are not compatible with the new motherboard. So, before it can boot normally you have to either repair install (also called reinstall) Windows XP, or preferably do a clean installation.
Installing Windows XP - Full tutorial
http://www.dedoimedo.com/computers/install_xp.html
ProduKey v1.65 - Recover Windows product key
http://www.nirsoft.net/utils/product_cd_key_viewer.html#DownloadLinks