no, you can do a direct swap with identical mobo, cpu, etc,
but an upgrade will require new drivers to work properly and
many changes will prevent booting at all, such as going from
Intel to AMD.

At the very least you'll have to do a "repair" installation.

My experience with replacing a motherboard and doing a repair installation
is that a reformat and completely new installation is to be preferred.

YMMV.

Greetings --

  Normally, and assuming either a retail license or a generic
(non-branded) OEM license, unless the new motherboard is virtually
identical to the old one (same chipset, same IDE controllers, same
BIOS version, etc.), you'll need to perform a repair (a.k.a. in-place
upgrade) installation, at the very least:

How to Perform an In-Place Upgrade of Windows XP
http://support.microsoft.com/directory/article.asp?ID=KB;EN-US;Q315341

   As always when undertaking such a significant change, back up any
important data before starting.

Bruce Chambers

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having both at once. -- RAH

My trick is to always use new motherboard with same chipset munufacture. I
use SIS chipset. Went from 645 to 645DX to 648 without any trouble.

If trouble:
http://michaelstevenstech.com/moving_xp.html#4

-Kent

my experience:
via chipset to via chipset..ok
via chipset to nforce chipset..total failure