wmp and update problems

I run windows xp mce. I can't install wmp11. everytime I try, it says "It was not possible to complete setup. For more assistance, click web help." and "Windows Media Player 11 was not installed. To update Windows, run Windows Media Player 11 Setup again." Running again produces the exact same result. web help directs me to this highly unhelpful page. The wmp11 installation also appears to uninstall wmp10 and its codecs, but not all the time. I'm not really sure what's going on there.
also, I can't get update KB913800. It's on my computer, but it won't install, automatically or manually. Automacit Update gives the unhelpful message "The following updates were not installed: Update for Windows XP Media Center Edition 2005 (KB913800) ", and has a button to close.
My problems seem very similar to this guy's, but since his are apparently unresolved, so are mine. Any help?