I'm running a minimal system at the moment, just XP with a dozen or so essential apps, no e-mail client (webmail if needed), no software
firewall (hardware in router). This thing boots really fast and feels light as a feather in daily use. I also found the perfect antivirus companion for this spartan setup: BitDefender 8 Free Edition. The Virus Shield option is not available, but you do get automatic updates and can scan what-/whenever you want. After 10 years Internet and with some common sense, I'm comfortable with that. For the inexperienced, I'd recommend AVG (first or Avast! second).