Why are you attempting to use Windows XP as a diagnostic tool?
There are lots of other tools I would use over XP for diagnostic tasks. The first that comes to mind is the Ultimate Boot CD. It comes with lots of great diagnostic tools.
As to why XP has problems when you use it with different hardware, there are 2 reasons for that.
1 is that the XP license is tied to the hardware your copy of XP is installed on and activated with. In fact, if you are using a retail or OEM licensed copy of XP, using it on multiple computers does violate the EULA.
The second reason is that XP uses a Windows NT based core. A critical system file (HAL.DLL) is built up specifically for the hardware of the computer it is installed on. This is the Hardware Abstraction Layer. This is the same reason that when you pull a hard drive with Windows XP installed on it and move it to a different computer that the system does not boot into Windows.
Chas