Hi, I'm a Mac

Robert Vamosi has an article in PCWorld about 'securing' your Vista-based PC:

While Windows Vista may be Microsoft's most secure operating system ever, it's far from completely secure. In its fresh-from-the-box configuration, Vista still leaves a chance for your personal data to leak out to the Web through Windows Firewall, or for some nefarious bot to tweak your browser settings without your knowing. But by making a few judicious changes using the security tools within Windows Vista and, in some cases, by adding a few pieces of free software, you can lock down your operating system like a pro.
For a quick overview of your security settings, the Windows Security Center is where you'll find the status of your system firewall, auto update, malware protection, and other security settings. Click Start, Control Panel, Security Center, or you can simply click the shield icon in the task tray. If you see any red or yellow, you are not fully protected. For example, if you have not yet installed an antivirus product on your machine, or if your current antivirus product is out-of-date, the Malware section of the Security Center should be yellow. Windows does not offer a built-in antivirus utility, so you'll want to install your own. For free antivirus, I recommend AVG Anti-Virus 8.
The Malware section also covers antispyware protection, and for that Windows Vista includes Windows Defender. The antispyware protection in your antivirus program usually trumps the protection Microsoft provides, but there are several good reasons to keep Windows Defender enabled. One is that every antispyware program uses a different definition of what is and what is not spyware, so redundant protection can actually offer some benefit.
Another reason to keep Windows Defender enabled: diagnostics. Click Tools, and choose Software Explorer from the resulting pane. You can display lists of applications from several categories such as Currently Running Programs, Network Connected Programs, and Winsock Service Providers, but Startup Programs is perhaps the most useful. Click on any name in the left window, and full details will appear in the right pane. By highlighting, you can remove, disable, or enable any of the programs listed.

Rico says there's more, but he can't be bothered to get it for you; click the post title if you need to read it. Or buy a Macintosh and have done with it...