I have 40+ Macs 10.5.x and 10.6.x, all connecting and maintaing a connection fine
Blackberrys, iPhones, Google devices all fine.
yet having trouble with 3 Windows based devices

Advent laptop: Windows Vista Business SP2, 802.11b/g Mini Card Wirless Adapter (built in) can see the wifi name, enter the corect WPA passkey and it says unable to connect
Samsung Netbook: Windows 7, same as before can see the wifi name, enter the corect WPA passkey and it says unable to connect
Toshiba laptop: Windows Vista Home SP2, 802.11n REALTEK RTL8191SE (built in), connects but drops off the network after periods of time. (I've since turned off power saving on the card to see if this improves stability)
any thoughts or suggestions?
TIA