Ever hear the saying "If it seems to good tom be true..."?
I have no idea about this specific site, but many of these are in
foreign countries where it is impossible to deal if you have problems.
Buyer beware.

Many folks have posted to this newsgroup have been "scammed"
by an "offer to good to be true".  All I can say is you take your chances
and if you encounter a problem (i.e. Product Key does not work), you
are on your own.  That particular website offers no "contact information"
so that should raise a huge "red flag".  Chances are high you'll end
up with an expensive "coaster" and have zero recourse.  The site also
claims the software is "shipped from Eastern Europe" so you may
get Windows XP written in Polish with English subtitles.

there are some liscense resellers out there, all you get
is the number to use on your existing cd's. For example,
home user with 3 computers. You buy once, and get the cd,
then buy a resold liscence, and get to install again on
another machine fairly cheaply. They send you the actual
M$ sheet with the number and funny printing and junk so
you can show that you own the liscense if anyone asks.