On the Intel 2200, 2915 and 3945 drivers, there is a Power Management setting.
Set it to "highest" or max performance. This burns the laptop battery faster as the wireless card stays on. But, it also stays connected to the trapeze/nortel access points.
Beware of the windows xp feature "repair". It may reset changes you make to the driver to default.
If your T42's have Intel 2200's wireless nics and drivers dated 2004, I would update the driver. I've seen roaming issues with those drivers.