For 802.11b and g, there are only 3 non-overlapping channels. So that means if you have 4 or more access points within range of each other you will have interference. 4 isn't so bad, but 8 is a lot.

My best answer would be to get an 802.11a access point which uses the wide open 5GHz spectrum. No interference worries there. That means buying a new AP, but that may be your only choice.