I have been searching all week for a solution. I found so many people with the no wireless networks problem when they switched to Windows 7 (just like my experience). Well, my solution was to repair my Kaspersky anti-virus installation. [I cannot remember the site I found the information on to give the person credit. I am immensely greatfull though.]
  Additional setup info:   Dual HDDs (Win7 Pro & XP Pro) XP Pro – LAN & WiFi work fine (orig. configuration from Dell) Win7 – neither LAN nor WiFi work (Win7 added after purchase)   I was working on setting up an outdoor WiFi antenna a couple of days ago when my problems started. I was working in Win7, which I had not been using that often. My LAN connection was not working, and I realized the driver had not been installed. I downloaded it from Dell’s website and installed it. I received an error message about SNMP service not being installed. I turned the service from disabled to auto. I do not know if my LAN adapter is now working. That is my first problem.    My second problem happened when even though my WiFi card had been working fine, I decided to see if its driver had been updated. It was not. I believe a Microsoft driver was installed. It was working just fine though (smile), so I had to mess with it. I downloaded the driver from Del’l's website and installed it. That is when my problems started. The WiFi card has not worked since. First I realized I installed the wrong driver. I uninstalled it and installed the correct one. I even restored the system to before I messed with any drivers. No luck. My WiFi card still does not work. The Intel utility states it fails the hardware test and passes the driver test. Win7 states it cannot find any wireless networks (if I switch to XP Pro everything works). I am at a loss and very frustrated. Can anyone help me please?   On the WiFi card, Win7 thinks there might be a problem with the driver (I have tried re-downloading & re-installing it, which did not resolve the problem). Win7 also states “Windows couldn't automatically bind the IP protocol stack to the network adapter.” Everything looks fine in the device manager. 
Dell Precision M6400 laptop w/Intel 5100agn WiFi Card – hardware failure, 
driver ok, no