That's easy. Just use Grissoft's AVG or Avast! 4 Home. In fact, you can download, install and use both together. No conflicts between them, and they both perform right well, although for the present I would have to say that Avast! 4 Home seems to be in the lead for getting automatic updates and letting you know that it got them. Might run a shade better as well, but AVG seems to have a good handle on scanning emails for bad attachments.
What else is there? Well, you see a lot of ads for this or that sometimes, but some are very questionable. Best find a place where each is rated against the others in order to get the best one.
What else? Amazing thing if you decide to step forward to installing Ubuntu or some other version of Linux on your PC, either making a dual boot process or replacing Windows. I like Ubuntu particularly, as it is really easy to pick up on It's harder if you want to go the dual boot route, so best find articles and posts that explain how, if you are not into manually setting up drive partitions.
Linux is immune to attacks focused on Windows. And if you still want Windows, you can have both running together, Ubuntu is your host OS, then you add and use VirtualBox (free to individuals) which will let you install Windows as a guest OS as well. You can then either run just Ubuntu, or call up VirtualBox and tell it to start up Windows in what was once called a sandbox. There, even tough Windows and any installed applications with it work as expencted, to the outside world it still looks and acts like Linux, because Windows service calls are being redirected by VirtualBox to equivalent Linux services. Man, this is like being behind a moat and a juge stone wall! Hardly anything can get to you, and I've been doing this for a year without any added protection and yet my system has been scratch free from outside forces. Windows even runs faster as a client without the software protection bloat, and you can even use copy and paste between applications under the two OSes without a problem. Fact is, Linux can handle FAT, FAT32, and NTFS partitions and files without a sweat, and you can even add a driver to windows so that it can work with the Ext3/Ext3 partitions and files commonly set up by Linux. So it is a back and forth world, and you can click between them with a single mouse action. Might take you two weeks to get it all working together, but it is really worth while. Just a thought.