In my Inspiron 600m, the Truemobile 1300 WLAN mini-pci card is now working correctly. I had reported here before that it couldn't detect any wireless network even though device manager reported it was working properly. I spent two hours on the phone with tech support today (four different technicians) until Julia in Wireless support led me through some further checks.
It seems to be the settings in the "configure" under the identification of the wireless card under wireless networking. The key problem may have been that Bluetooth (not installed on this machine) was set for "Enable." When changed to "disable" the wi-fi card recognized the access point.