I've recently run into a problem where attempts to update XP/SP3 from the Microsoft update site are blocked by DEP. This is puzzling to me because I'm under the impression that DEP applies only to Vista (and maybe W7), but not XP. Any insights on why this is occurring and what I can do to keep my system updated would be deeply appreciated. 1 person needs an answerI do too

DEP is part of Windows XP SP2 and newer. You might consider checking and manipulating the DEP configuration. Also consider scanning for malware