The odds are good that the Windows installation won't start in the new
system, unless the mainboards are identical.
It's supposed to be possible to remove some of the old drivers (in
particular, the IDE drivers) in the old system. When the drive is used in
the new system, the appropriate drivers would be auto-installed.
I've never done that, myself. I have used a repair installation. (This may
not be possible if you have an OEM XP CD, rather than a retail version.)
http://support.microsoft.com/default.aspx?scid=kb;en-us;315341
"How to Perform an In-Place Upgrade (Reinstallation) of Windows XP"
(In brief: change the BIOS settings to boot from the CD first. Boot from the
XP CD. Choose install rather than going to the repair console. Under
installation, choose to repair rather than a new installation.)
This ought to preserve most files and settings. (It's not guaranteed, so a
backup is recommended.) You will lose everything installed through Windows
Update, unfortunately.
Either way, you'll probably have to re-activate. I don't know how this works
outside the USA, but here, if it has been longer than 120 days since the
last activation, the new one can be done over the Net as if it was a new
license. If it has been less than that (or, as has happened to me, the
drivers for the new NIC weren't installed), you'll have to activate by
telephone. (In the States, it's a toll-free call.) You'll have to explain
the upgrade to a Microsoft representative, emphasizing that it will be used
on only one machine. The process is tedious, but it only requires five
minutes.
Good luck.
Bob Knowlden
Address may be altered to avoid spam. Replace nkbob with bobkn.