I manually downloaded the update, booted into Safe Mode, ran it, it said it completed. So here I am, back in normal WinXP Pro and it's still listed as one of my updates at Windowsupdate.com! At the same time, it's still listed as successfully completed in the installation history.
*edit* Uninstalled it from Add/Remove programs, reinstalled it manually, still shows up on Windowsupdate.com; bah!