have you tried a wireless scanner like kismac (mac) or netstumbler (win)to see your signal strength?
sometimes raising the router up a little higher can yield better results and tweaking the antenna.
11mbps wireless is not that great and the slower of the two receiver cards usually hampers the other.
have you fed the router both mac address details and only allowed the router broadcast to connect to these mac address's?.
every time i set these up for clients i see a improvement in seek and download times with this method activated.
alternatively someone in your area might have a router that blankets the area with their signal, like
mine
when i do file transfers it cripples anything around in my area, by hogging all the available spectrum.