An easy way to protect yourself against viruses is to setup multiple user accounts when setting up windows. Setup an administrator account that has full privileges. Then setup a regular user account that does not have installation program rights.
You would simply use the regular user account for your everyday computer usage but you could switch to the administrator account when you need something installed. This adds an extra layer of protection from viruses and malware. Most of these programs will try to install themselves (usually from a website) but if the account browsing the website does not have the privileges, the virus/malware cannot be installed.
If you already have installed windows, it is not to late to change to this configuration. Simply create your administrator account. Log in using this account and remove the privileges from the other active accounts.
Remember, layered protection is the best way to prevent malicious code from infecting your PC.