This worked for me on a Dell Latitude D800.
Installing Intel Pro 2100 wireless LAN driver on windows 2003:
1. Download the windows XP driver from Intel's (or Dell's) site:
{Most likely, you received this driver with your laptop}
2. Extract or copy the driver files into a temp folder:
3. Goto Device Manager, select the driver-less "Network Controller" and choose "Update driver"
4. Next dialog, choose "Install from specific location..." and select the temp folder from step 2.
Hope this helps.