Unfortunately, this Microsoft service will soon be discontinued - what a shame!
Good luck with that!
I haven't done a thorough research yet, but if you look at this link
Windows XP might loose antivirus updates for Security Essentials after April 2014 - Techworld.com
so there is clearly only from MSE updates for WinXP the speech. And that's understandable, since people who want to keep XP running don't think they are still safe thanks to MSE.