Maybe it is just my computers, but does AntiVirus monitoring slow your computer down significantly? It is almost more trouble to me when it is protecting my computer.
Try this security setup it will use less resources then either of those:
I suggest you run 1 Anti-virus program/ 1 Firewall/ and a combo of anti-spyware
Firewalls
Here are some firewalls which are free for personal use and most commonly used: Comodo <-Vista Compatible Kerio (sunbelt <- vista compatible Online Armor Zonealarm <-Vista Compatible I recommend this one