Hi GoldKnight! ^_^
*coughs at chat last night*
I highly recommend Kaspersky Anti-Virus. I was introduced to them about 2 years ago and they have been great. I haven't experienced any slow-downs with my computer at all, especially since I run real high-memory programs such as Paint Shop Pro, AIM, and other programs.
They have a free virus scan you can use to test it out here:
http://www.kaspersky.com/virusscanner
And if you are satisfied, just go to
http://usa.kaspersky.com/downloads/trial-versions.php to try out one of their trials to get a feel for it before you buy it.
They are a little lesser-known than McAfee or Norton Anti-virus, but all the computer geeks that I hang out with (I consider myself a computer nerd) highly recommend the program.
I hope this information helps!

*glomp*