The HDD from your old/dead PC has XP installed
with a number of device drivers that are specific
to the old motherboard.
When you wire that HDD to a new motherboard,
XP will try to boot, but you will almost surely
get a number of error messages about missing
XP may be able to locate the missing drivers,
if you insert the motherboard's Support CD
during that first boot attempt.
Another/additional option is to try connecting
that new motherboard and old HDD to the
Internet as soon as possible, and then running
Some of the missing drivers may be found
by Windows Update.
But, THE single most important set of drivers will be
the chipset drivers that are unique to your new motherboard;
those chipset drivers should come on a Support CD
that is packaged with your new motherboard.
Alternatively, those chipset drivers should be
available for download from the website of
the motherboard manufacturer.