Expander vs Router Connection Confusion

Question

For some reason, while all of my wireless laptops sees the closer Expander, some of the laptops connect to the farther-distanced base router instead.
Let me explain.  When I "View Available Networks" in Windows XP with expander not powered up and only the router, my available signal is really weak when I position myself at the outer rim of the router range.  Once I powered up the Expander (matching SSID Setup already done) and Im positioned at the same outer range of the base router, I get same SSID but I get full signal now.
Some of my laptops will connect and show the increased signal.  The speed in surfing is evident too.  However, some of my laptops will show the stronger (ie closer Expander) but upon connection will revert to the signal strength and slower speeds of the times when only the router was connected.
How come? I have four laptops at home.  Three are exactly the same make and model.  However two of the same will first "see" the Expander when "Viewing Available Networks".  However, upon connection,  the signal would certainly suggest that two of the four laptops have connected to the router as if the expander was not powered up.
WRT54GS - Firmware 7.5
WRE54G - Firmware 2.01.10
Both have already been set up and have the same SSID and Channel.  Same Subnet and Gateway.

Answer 1

Thank Dibbler,
Looks like this issue might be the notebooks' wireless adapters.
I had a Linksys PCMCIA Wireless Card lying around.  I wanted to see if I could wirelessly connect via the PC Card instead of the the internal.  At least for the moment, Im getting a steady connection and speed.  Although taking the only PC slot and having the card stick out is kind of an annoyance.
One of the clues was when I was using inSSIDer wi-fi scanner utility on the non-working and working notebooks in the same location, I was getting vastly different signal scan readings.  Whereas the working notebooks generally had very steady and strong signals for many different wi-fi broadcasts in the area, the problematic notebooks had extremely fluctuating readings from most signals that could be scanned.
As I alluded to my inital post, three of the four notebooks are the same make and model.  Although, the two of three actually has a different built-in wireless adapter vs the third which wifi works fine.
Problematic adapter is a the Intel Pro\Wireless 2200 which after some research surfing appears to have exhibited this problem for number of years now with many people.  Has something to do with the a very aggressive "Power Save Polling" which the adapters continously powers down to conserve battery. However, the Intel process or driver appears to degrade the speed and connection over time.
I tired going into the Wireless Properties - Configure Settings to turn-off or negate the Power Saving Features, but there appears to be no change wifi quality.  Dont know if the current driver or software is even allowing me to change the adapter to Max Performance Settings.
Some posts from other tech sites suggests going back to an older driver (no use upgrading as I currently have the latest driver for the notebook adapter) to fix this problem though not everyone seems to have their connection fixed with a driver rollback.  Also the suggested older drivers are not available from the Intel site and I cant find a third-party with the suggested driver.
I hope to find a way to eventually tweek the Config settings on the internal adapters to the point that problem no longer exists, but for now I got at least one more notebook working because of the available PC Card.