here's some more info:
http://www.experts-exchange.com/Operating_Systems/WinXP/Q_20292761.html
>The problem that some folks are missing here is that there is a thing called the HAL which is compiled in a dll. The hardware info and SID are not just housed in the registry >anymore, the hal.dll is part of the deal and can't easily by bypassed. That is the reason for my first post to point out that one needs to do things to be able to move an XP >installation from one machine to another. I also pointed out to use the SysPrep utility because that is its function, which is to prepare moving the XP installaion from one >machine to another.
>
>By just moving the HD to the other machine XP will probably choke just on the fact that the mother boards and the CPU are completely different. They will have different >check sums and serial numbers not to mention probably a different bus architecture and few other gotyas and for XP these are consider major hardware changes. I know by >experience that it will only be pure luck to take a HD from one machine and plug into another machine with Win2000 or XP installed on it and have bootup into the OS.
>
>The first link I posted outlines how to move a current XP installation from one machine to another. One of the things it mentions is to use NTBackup as way not only for >backing up the current installation but how to use it to preprare for it to be installed onto another machine. It outlines what one needs to do step by step. It sort of implies >that a second HD is part of the mix.
>>>In this case, what should I care about SID
>You have no choice in this. It has very little or nothing to do with networking. Since the SID is contructed partly based on your hardware and this hardware isn't going to be >a match on the new machine so XP will see that the SID probably is incorrect and will probably not boot.