Wireless card device driver for Dell Inspiron 6400?
 

Where can I find the driver for the wireless network card for Dell Inspiron 6400? thanks!!

First find out which controller it uses.
Try "lspci -v". Then use google to find which kernel module you need and if you need a windows driver as well.
Some devices need firmware cut out from a driver written for windows. Some can use a native linux driver and don't need firmware. If there isn't a kernel module that handles the chipset, check if ndiswrapper supports it which wraps a windows driver in it's entirety.

Broadcom devices probably use the b43 kernel module ( b43-fwcutter needed to cut firmware )
Older atheros devices can use madwifi. Newer atheros drivers will use ath5k or ath9k. These don't need firmware.

Please put your distro in your user profile so we don't have to guess which distro you are using.