Thanks, Richard. Funny thing, I went to Windows Update to do this (they said it was available there) and there's nothing to be found. Did all the Critical Updates, but not SP1 installed. Hmm. Just pointing it out for those who think they may have gotten it via Windows Update...
I got it via Windows Update (for WinXP) this morning. I don't think it was in the Critical Updates section, though (which, for XP, are the only ones selected for download by default). I had to click on one of the other sections and add it to the list of items to be updated.