No, seriously, speaking as someone who installs
- Ad-Aware
- Spybot Search & Destroy
- Mozilla Firefox
- Mozilla Thunderbird
- ZoneAlarm
- upgrades to XP and then service pack 2
- Grisoft's AVG or Alwil's Avast 4 Home Edition (free anti-virus software)
- a hardware firewall/router between machine and internet.
on relatives' machines, hides Explorer and Outlook express, and then regularly checks that they're keeping these multiple products up to date with the most recent updates and makes sure they're tech-savvy enough to not double-click or accept things that they shouldn't, my advice is: get a Mac! They are well worth it.
For less advanced usage--email and web--a Linux desktop will do just as well, but it takes a bit more savvy to set up for a user in the first place.
(And some people have the gall to say that "Open Source Software is only free if your time is worth nothing.")