I have the same problen with a Dell Lattitude E5500 withthe 5100 AGN. Did you ever get a resolution to this?
I have tride changing the drivers. I have installed and removed all the drivers for my machine from Dell, and have installed the drivers from Intel for the 5100 AGN. All ofthem connect momentarily to the Router and then drop off. THe Diagnoses sas it did not recieve an address. I have connected a Netgear WDNA3100 USB wifi addapter to the laptop and installed the drivers for it. As soon as I typed in the security code and clicked ok using the Netgear adapter connected. This leads me to belive that the drivers for the 5100 have a code issue, Perhapse a timing issue in recieving the DHCP.
I have searched the web on a solution to this problem, but have found no answers.