the process is called
downgrading
the process is not
unlike upgrading,
except you would
require an installation
cd with the older
o.s. on it to downgrade
your system.
it is because the o.s. are
separate and unique
operating systems even
though they are made
by microsoft.
if your system came with
the older system on it,
then i highly recommend
figuring out where it came
from.
if your system came preinstalled
with an o.s., then it would
be a good idea to get that
software from your computers
homesite/maker.
also, there are cases that if a
system came preinstalled with
windows, there might be a
holographic sticker on your
system with the product id
number.
in any case you should also
review the homesite to see
if they provided your o.s.
installation files and specialty
software/drivers and stored
them on a hidden partition on your
harddisk, instead of providing
you with the physical cd's.
otherwise, if your system is
not one of those like the above
then you might simply have
to purchase a new set of
win xp installation cd's and
obtain a new license.
let us know what you discover.