Create a password for the Administrator account. You can find the option under Start, Settings, Control Panel, User Accounts.
Password-protect your screen saver. Go to Settings, Control Panel, Display. Click the Screen Saver tab. Change 'Wait time' to 5 minutes, and check On resume, password protect. The password will be your user password.
Turn off file sharing in Windows Explorer. Open Explorer, click Tools, Folder Options, View. Scroll to the bottom, uncheck Use simple file sharing, and click Apply.
Turn off the Windows Firewall. Go to Settings, Control Panel, Windows Firewall and click off under the General tab. Then, install a software firewall such as ZoneAlarm.
Turn on Automatic Updates. Go to Settings, Control Panel, Automatic Updates. Select the first option to have each update download and install automatically. If you want more control over the process, use either option two or three.
Install an antivirus program, turn on automatic updates, and set up a regular scanning schedule.
Install an antispyware app and run it on a regular schedule.
Turn on your browser's pop-up blocker. In IE 7, go to Tools, Pop-up Blocker Settings, and choose the Medium option (this is the default, but it's easy to turn it off accidentally); to kill all pop-ups, select High.
Optional: Set a BIOS password in your PC Setup application.
Optional: Increase your browser's security settings. In IE 6 or 7, click Tools, Internet Options, Privacy and move the slider to High.