| do you have the right drivers for the card?|
it was shipped in two versions,
Dell Wireless 1390 802.11g Mini Card Wireless
and also a intel card called
Optional: Intel® Pro/Wireless 3945 802.11 a/b/g Mini Card Wireless
i don`t remember if dell has there own program for wireless.
hope it was that.
try a another wireless card. "usb"
see if it works.