Stay far away from any Norton software though, it's generally not as good by far and more expensive.
And all generalisations are false.
Some quick ideas on securing a WinXP client:
1. Only log on with admin rights if you need them. Create a "power user" account for day-to-day use.
Why? If you accidentally run some malware, it won't have local admin rights.
2. If other people ever use the machine, create separate accounts for them. No ifs, no buts. Never delete an account when obsolete - just disable it. Also, in this scenario - or if you worry about local data being accessed by someone who steals the PC
- seriously consider using EFS.
3. Have a quick look at Control Panel > Admin Tools > Local Security Policy. The range of options and setting is baffling, but you can avoid hours of study by using a readymade security template; alternate-click on Security Settings, then Import Policy. "hisecws" is most secure but also most likely to break features; "compatws" is the opposite, and "securews" is in the middle of the spectrum.
4. Go to Control Panel > Admin Tools > Services, and set the following services to "Manual" (unless you need them for something specific):
Remote Registry, Routing & Remote Access, Error Reporting Service, Print Spooler (if you don't have a printer), Secondary Logon, TCP/IP NetBIOS helper, Windows Time, WZC, ALGS, Application Management, Terminal Services (if you never need fast user switching or any kind of remote desktop).
If you're especially paranoid, and you're sure nothing is dependent on them, then set them to "Disabled".
Hope that helps!
These things are all free, and only need to be done once.