Microsoft Update will supply you with updates to XP and MSE, just make sure not to install the last MSE update. Avoid KB2949787. Otherwise you will get the red MSE icon and the warning box every startup. If Windows Update offers updates, do them manually using the customize option. Unchecking an update hides it from later being added. You can update them later by going to the MU site and checking for all updates. Then look at the Hidden Updates to restore them.
MSE can still be updated in the application so far. I don’t know if there may be other KB updates sent, but MSE will supposedly still be updated with new definitions which may also be done manually inside MSE.
You may be able to uninstall the KB update too! I posted this in another thread but I think it may help a lot of users. I’ve been using MSE because it is supposed to still be updated by M$
MSE updates do not update the XP OS, just MSE. Updated Definitions should still help.