|XP is not readily transported from one machine to another.|
Putting aside the EULA provisions that stipulate OEM licences are tied to the machine they came with, there is the problem of hardware. The operating system is configured for the hardware environment in which it was installed. If you transplant an XP or later operating system drive into a different hardware environment you will have to perform a repair install ( unless the new hardware environment is an almost identical match for the old) .
Do you have an XP Install disk? If not then forget it. If you do have one then why not just do a clean install in the other PC?
Goin' Fishin' (Some day)