I had the same problem with my wifi card (Intel Pro Wireless 3945 ABG) on my inspiron 6400. It's easy to find a driver for your wifi card (if you have the same card as me just follow this link: http://downloadfinder.intel.com/).The main problem is, depending of which linux distribution you are running, you may not have the right kernel (that was my problem with mandriva 2006).At this point you have two choices:
you can upgrade your kernel or change your linux distribution for a newer one
(for exemple i have tried mandriva 2007 and it works).

ok thanks but i think my wifi card is differnt but i'll look there

It's been a few days since you posed this question, so I was curious to see if you ended up figuring it out yet.

If you still need assistance, it would be helpful to know exactly which wireless card you have, and the Linux version you are using. i.e. Red hat, Suse, Ubuntu, Debian, etc.

To assist, you can use a command line to give us a look into the PCI devices you are using: "lspci"

You should see an entry regarding your Wireless Ethernet Controller.

Regards..