It's disgusting that you have to do all of that just to even begin to worry less. Even after all of that, you can't trust the OS.
I'd suggest jumping ship from XP, though. It hasn't been supported for a couple years now I think, so 0-dayz in the wild remain in the wild and pervasive.
I'm using a stripped version of XP called naked Windows XP so, its never been supported. I've never ran antivirus software or anything on it but I've been pretty good at keeping it secured.
You should try transitioning to Ubuntu or Qubes Linux. I think you'd like it!