Symptoms
You connect a Windows Vista-based computer to a network.
A router or other device that is configured as a Dynamic Host Configuration Protocol (DHCP) server is configured on the network.
The router or the other device does not support the DHCP BROADCAST flag.

In this scenario, Windows Vista cannot obtain an IP address.

Cause

This issue occurs because of a difference in design between Windows Vista and Microsoft Windows XP Service Pack 2 (SP2). Specifically, in Windows XP SP2, the BROADCAST flag in DHCP discovery packets is set to 0 (disabled). In Windows Vista, the BROADCAST flag in DHCP discovery packets is not disabled. Therefore, some routers and some non-Microsoft DHCP servers cannot process the DHCP discovery packets.

Resolution

Summary

1. Use getmac and ipconfig /all to determine the GUID of the adapter that is having the problem.
2. Set the following in the registry:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID}
   Value name: DhcpConnForceBroadcastFlag
   Value type: REG_DWORD
   Value data: 0
   Note A data value of 0 disables this registry entry. You can use this registry entry to prevent Windows Vista from using the DHCP BROADCAST flag. After you set this registry entry, Windows Vista never uses the DHCP BROADCAST flag.

Details

1. Start, run, cmd
2. Run ipconfig /all
   You'll get something like this:
   Ethernet adapter Local Area Connection:
      Media State . . . . . . . . . . . : Media disconnected
      Connection-specific DNS Suffix  . :
      Description . . . . . . . . . . . : Intel(R) PRO/1000 PL Network Connection
      Physical Address. . . . . . . . . : XX-XX-XX-XX-XX-XX
      DHCP Enabled. . . . . . . . . . . : Yes
      Autoconfiguration Enabled . . . . : Yes
   Note the MAC address of the wireless adapter (shown here with XXs).  Note this is a WIRED adapter in this example; you want your wireless NIC.
3. Next, run getmac
   Match the MAC address to the GUID of the adapter.
   Physical Address    Transport Name
   =================== ==========================================================
   XX-XX-XX-XX-XX-XX   Media disconnected
   YY-YY-YY-YY-YY-YY   \Device\Tcpip_{F37508DE-020D-43A3-916A-ED3EE080C910}
4. Click Start, type regedit in the Start Search box, and then right click on regedit, and choose "Run as Administrator"
   If you are prompted for an administrator password or for confirmation, type your password, or click Continue. 
5. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID}
6. In this registry path, click the (GUID) subkey that corresponds to the network adapter that is connected to the network.
7. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
8. In the New Value #1 box, type DhcpConnEnableBcastFlagToggle, and then press ENTER.
9. Right-click DhcpConnEnableBcastFlagToggle, and then click Modify.
10. In the Value data box, type 1, and then click OK.
11. Close Registry Editor.

See also: http://support.microsoft.com/kb/928233