PC gamers don't have it easy. Alongside the constant hardware arms race and GPU penis-envy, you have the problem that your platform of choice might not just be used for gaming. Even in a locked room with no interwebs a Windows PC is like a magnet for malware and viruses. What's worse, the remedy for such net.bastards - anti virus software - can slow your PC down and hog precious memory.
Antivirus stalwarts Norton feel your pain and will try to offer succor in the form of Norton AntiVirus 2009 Gaming Edition. The release is tweaked to use 80% less memory than the standard settings and will allow security parameters to be dialled down to maximise performance.
There is also a 'Gamers Mode' that suspends all update downloads (no bandwidth sucking while you are trying to use your link for sensible stuff like killing Zombies) and stops all antiviral notifications from interrupting your playtime.