or Word Viewer 2003?
Just checked and discovered I'm running Word 2002 SP3 on this box (that's another one that wasn't on my list), so some time in living memory that must have asked me to download the SP3.
And ... er ... I rather suspect that there are lots of people running XP but with rather older versions of Office ... being ones that are easier to copy than the newer versions.
Now if the original question was about SP5a then that'd have been easier, so far as I know there was only ever one of those ... whoops, no, there were several of those too.