It's a bit disappointing really. I though a 108G router with so called SuperG turbo will solve my problem here. This is the speed test I did yesterday using speakeasy. Today I tried to move the router around to see if signal strength improves. To my disappointment it's still very directional, i.e. my notebook facing different direction will get very different results.
Another way to monitor connection speed is to use "ping 192.168.0.1 -t". I can see the response time could be 1ms to 24ms or even request time out. The graph on the right shows how signal strength changes on turning my notebook by 90 deg, this is done by running a freeware Network Stumbler. Warning: don't use NetStumbler and the ping method at the same time as ping response is affected when NetStumbler is running.