are you moving around with the laptops when their connection speed(s) change? are there microwaves, old cellphones or cordless phones in use? Have you tried changing the channel of the router itself from the default?
Furthermore I am more the 50 feet from the router 4 rooms away.
maximum range of standard Wireless-G is about 125feet or so; I don't see how you can get the full 54mbps at half that distance.
Either way, your laptops are not "speed-hopping" in any way. That speed indication (I assume you are using the tooltip from the network icon in the notification area or something similar) is merely a estimate made by the computer based on your Signal strength. Your problem is a intermittent signal to noise ratio. I've encountered similar problems and they were always fixed by simply changing the channel of the router from the default.
