What wireless modes are you using?
Try single mode G or mixed G and N?
What security mode are you using? Preferred security is WPA-Personal. WPA2/Auto TPIK and AES.
What wireless devices do you have connected?
Any cordless house phones?
Any other WiFi routers in the area? Use
InSSIDer to find out.
Turn off Short GI and Extra Wireless Protection if you have it. Under Advanced/Advanced Wireless.
Turn off all anti virus and firewall programs on PC while testing. 3rd party firewalls are not generally needed when using routers as they are effective on blocking malicious inbound traffic.
Turn off all devices accept for one wired PC while testing.