We have 5 different laptops in the house, 1 macbook, 1 Compaq, 3 dells, plus numerous little devices like ipods, squeezeboxs, squeezebox radios and controllers, you name it.
All of them connect to and stay connected to the "downstairs" WIFI just fine. But my laptop (the most expensive of the lot) refuses to stay connected, preferring the much weaker and slower signal upstairs.
My laptop is running Win7 (64 bit) Ultimate with an Intel 3945ABG WIFI contoller (It's a Dell Precision M6300). The WIFI Access Point is a Cisco WRT54G2 V1 with firmware:
Firmware: DD-WRT v24-sp2 (10/10/09) micro Time: 11:11:10 up 42 min, load average: 0.06, 0.01, 0.00 WAN: Disabled