The best thing any Windows user can do to protect their PC from the getting infected from the Internet is to create a second user account with administrator privileges and to change the working user account to one with only limited user access. I promise you if you do so, your chances of picking up some web-bug, or virus are probably 99% less no matter how good your anti-virus program is. This is because a virus or malware cannot modify your Windows registry, nor can it copy itself into your Windows system folders if you work as a user with limited privileges. A simple reboot will kill any virus that may invade into the PCs memory.
The purpose of the Administrator account should be only to install software or to do certain tasks like changing the time or date, or to de-fragment the hard disk. It should never be used to browse the Internet! Probably more than 90% of all Windows users (especially Windows XP users) browse the Internet with Administrator privileges. It’s no wonder their PCs get infected, perform slower and sloooower, and sometimes come to a grinding halt!