Dell wireless 1390 WLAN mini-card malfunction

I have a Dell Inspiron 6400 laptop running and with a Dell 1390 WLAN mini-card installed and a Broadcom 44/10x100 integrated controller.

Unfortunately I've never been able to get this laptop to function with my wireless Internet, and I strongly hope someone here will be able to help me. You're my last hope, guys!! 

Anyway, here's what happens: Everything's working out nicely, and the computer connects to the network smoothly. After 5-10 minutes of full and unproblematic Internet connection the computer crashes the wireless network i.e. the Inspiron and all other computeres connected to the network is disconnected and my wireless network no longer shows up on the list of available networks.

The network works perfectly with every other computer I've used with it.

I've installed the newest drivers for both the 1390 and the integrated controller from this site. And my Vista is of course also fully up to date.

On the advice of a friend, I've also tried turning the antennae settings to "aux" - Alas, to no avail.

Can somebody out there help me?

Yours,

Kristen