Dell stops releasing driver updates for a laptop rather quickly. However, the same hardware is found in other laptops, and often these drivers will install. Drivers can even support similar hardware which is not explicitly listed. For example, a driver's description may claim support for one wireless card, but the driver may support all of Dell's Broadcom based wireless cards. A while ago I fixed audio glitches in Vista by installing a newer driver for my Dell Wireless 1500 Draft 802.11n WLAN Mini-Card.
Today I found that Dell had a Broadcom Wi-Fi driver for Windows 7 (R242438), but that driver refused to install. The error message was: "No compatible hardware found. The software you are attempting to install is not supported on this system." Despite this warning, I could manually install the driver via Device Manager without any warnings. After a manual install, the wireless card worked, but I didn't have the utility which shows signal strength in the tray and other components.
Since the driver seemed to be compatible, I searched for a way to do a proper installation. The driver installer unpacks itself to C:\dell\drivers\R242438. In that directory there is a "DellInst.enc" file. It doesn't look like anything, but it may be decoded via "BcmCrypt.exe" (also in that directory, USAGE: BCMCRYPT -e or -d <input> <output>). The file decodes into a text file which shows what cards are supported and what systems are certified with each card. The "Dell Wireless 1500 Draft 802.11n WLAN Mini-Card" (PCI\VEN_14E4&DEV_4328&SUBSYS_00091028) was supported, but my system was not in the list of systems in that section. I simply added the "0x01BD ;Inspiron 6400" line for my system and encoded the file with BcmCrypt. After that the driver installed properly and everything worked, although the highest speed seemed to be 130 Mbps. After changing some advanced settings in Device Manager, I finally got 270 Mbps.
While doing this I also found that there are three different drivers in three subdirectories of C:\dell\drivers\R242438. DRIVER_US is for the US, DRIVER_JPN is for Japan, and DRIVER_ROW is for the rest of the world. For example, it's possible to manually install the driver from C:\dell\drivers\R242438\DRIVER_ROW using Device Manager and gain access to channels 12 and 13. I never tested these channels and I now use the US driver which the installer installed, but it's nice to know that I can change that easily.