Recently purchased this computer, WinXP (sp2) and it came with the full Norton suite (which was a B to get rid of after it interfered with several other applications)
Using all freeware, hardly ever have any problem.
"Javacool's" Spyware blaster
AVG antivirus
AdAware
Spybot
CWShredder from Trend micro
Bazooka scanner
CCleaner
A2 scanner
The standard XP firewall.
Winpatrol
Hijack This.
All free and do a great job