I used to have a similar problem which disappeared when I got an Apple Extreme wireless router. Don't ask me why.
"I am disappointed and deeply concerned that there is no objective evidence to support my position. So far."
- Spock ￼
His: Intel iMac 20" 2.16 / Macbook 2.1 GHz / 8GB iPod Nano / 2GB iPod Nano / iPod Touch / iPhone 3GS / iPhone 4S
Hers: Macbook 2.1 GHz / 4GB iPod Nano / iPhone 4
Kid 1: 4GB iPod Nano / iPad 16WiFi
Kid 2: 4GB iPod Nano/ iPad 16WiFi
Family: iPod Touch / Apple Extreme Router 802.11n / Two Apple Express's w/Airtunes /Two Apple TV's 40GB / Apple TV 2