Wide connection speed range

I have an Inspiron E1705 with a Dell Wireless 1390 WLAN minicard. This connects to a Linksys WRT54G router. The problem I have is intermittent wireless connection speeds. The signal strength is always excellent but the connection speeds can be as high as the upper limit of 54 Mbps or as low as 24 Mbps. I know my internet provider can not transfer information at these speeds but whenever the connection speed drops below 54 Mbps webpages load slowly and downloads are almost unattainable.

What can cause the fluctuation in connection speeds? My router is not near any electronics. I have a desktop located on a different floor than the router and its wireless connection speeds never fall below the 54 Mbps.

Please help. Thanks.