Originally posted by: mechBgon
1) Install WindowsXP (I'm presuming you're using WinXP) and set a strong password on your Administator-class accounts. Consider making yourself a Limited-class account for daily usage, it's a nice safety net against malware
2) Service Pack 2 for WinXP, which includes DirectX 9.0C and a software firewall
3) Motherboard chipset drivers
4) Video and audio drivers AFTER motherboard chipset drivers
5) Install antivirus software
6) Now that you have a firewall and SP2 and antivirus software, plug into your modem (I'm assuming broadband) and update your antivirus software, and then hit Windows Update for a round of patches
7) If you have Office, install it and update it at Office Update
8) Install Microsoft Baseline Security Analyzer 1.2.1 and run it to evaluate your security
If you have broadband, you would also be smart to get a hardware firewall, in the form of a typical broadband router like a Linksys BEFSR41 or Netgear RP614, and that is a nice first line of defense against worms and script kiddies.
Hope that helps

There's links to mobo drivers, SP2 and some other stuff
here.