*addendum to this rule...
If you have a Windows XP CD that is "RTM" and contains *no service packs*
what-so-ever and you install using that CD - in order to install SP3 onto
that clean installation of Windows XP - in my experience you *will* need to
install Windows XP's SP1a or SP2 before you will be able to install SP3 on
top of it.
Even Windows XP SP3's own documents seem to point to this:
http://download.microsoft.com/downl...982/Overview of Windows XP Service Pack 3.pdf