Re: Latitude E6400, Intel Wifi Link 5300 AGN Drops Connections
FWIW, the Intel 5300 in my M4400 (same card as yours) supports WPA2.
I'm using WPA2 to connect to a "g" 2-wire 2701 router, and though I prefer TKIP (less intrusive polling) it connects fine with AES as well.
Default settings of Power Management - Highest, Roaming Aggressiveness - Medium, and Power Saving Mode - Off.
Latest Dell driver (184.108.40.206) but I uninstalled the included PROSet software.
You might try installing the Vista SP1 Wireless Feature Pack from the Dell downloads page for your system + OS; it seemed to help the stability of my WiFi as well as my BlueTooth connections.
I'm running a fresh install of Vista Business x64.
x64 Precision M4400/Quad QX9300/WXGA+ LED/8GB DDR2/256GB Samsung SSD/NVidia Quadro 770M/8xDVDRW+-/9 cell/EPort/BT/FIPS + Backlit KB/VZW-WWAN/56k/Intel 5300 a/b/g/n
x64 Latitude E6400/Duo T9400/WXGA LED/8GB DDR2/128GB Corsair SSD/ Intel X4500MHD/8xDVDRW+-/9 cell/EPort/BT/UPEK + Backlit KB/TEL-WWAN/56k/Intel 5300 a/b/g/n