Gamer or not, your system isn't performing very well if you are constantly infected with worms, viruses and Trojan horse programs that are easily preventable.

For starters, after you get the initial build online you need to go to the Windows Update site and download and install all applicable critical patches. You should apply Service Pack 3 and then any applicable patches after that.

You should also be running antivirus software. There are plenty of good ones- free, cheap and otherwise. I use Computer Associates on my home machines- but mainly because I can get it for free. I have used McAfee products with no problems. Find one, install it and update it at least weekly.

Lastly, you can have a firewall without impacting performance. While not the greatest firewall, if you buy a home Cable / DSL router they typical come with a basic NAT and port-blocking firewall. You can block all incoming ports except the port or ports you need to do your online gaming. If you have a spare computer you could also set that up as your firewall and connect through there. I use Zone Alarm software and I know many people like Sygate and other freeware / shareware firewalls. They are generally easy to configure and do the trick. I don't know how they are or how they compare in terms of using system resources though.

In the end though, I submit again that having your system compromised on a daily basis makes it much less effective as a gaming machine than any resource impact from running antivirus or firewall.