I was having problem connecting to the wireless network at work. Very frequently I noticed that my IP address was changed to the 169.254.*.*, an APIPA. When this happen, my laptop hangs for 5 minutes or more before it can attached to the wireless network again. It keeps toggling between the wireless network and the APIPA address.
I added this into the registry, HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters, "IPAutoconfigurationEnabled"=dword:00000000, which seems to have resolved the problem.