As others said above, I recommend that you update to windows 7 as windows XP is going to lose its support in 1 1/2 years.
I HIGHLY recommend that you replace Microsoft Security Essentials with Avast 7 Free, Avira Free, or Comodo Internet Security.
If you want to go for a paid solution, here are the ones I like:
Bitdefender Internet Security
Kaspersky Internet Security
Norton Internet Security
You should add some On demand Scanners:
Malwarebytes Anti-Malware
Hitman Pro
Emsisoft Anti-Malware Free
I would replace IE with any of these browsers:
Comodo Dragon
Firefox
Google Chrome