Picked up McAfee for "free" with BT. My old Acer, XP, SP3, half a gb Ram, seems to get along with mcAfee just fine. When McAfee does its scans, and its updates, whole pc is close to unusable, - it is certainly very slow, but when it is not scanning/updating it is fine. Not surprisingly scans are scheduled for when i'm not likely to use the pc, and updates happen when i switch it on, so i switch it on well before i plan to use it.