Most of you already know this, but
for those who do not...
If you go to Windows update be prepared
to deal with WGA...Windows Genuine Advantage...
MSFT will check your xp installed version to see
if it is genuine...if it is not, they will not allow you
to update;
however, The easiest way around this is to set
up your computer for automatic updates...
then you will be notified when new critical updates
are ready to be installed.
This is far easier than trying to use some unknown
software to out smart the techies at MSFT...