Windows Vista cannot obtain an IP address from certain routers or from certain non-Microsoft DHCP servers – http://support.microsoft.com/kb/928233/en-us
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
1. Click Start, type regedit in the Start Search box, and then click regedit in the Programs list.
2. Locate and then click the following registry subkey:
HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\ Interfaces\ {GUID}
In this registry path, click the (GUID) subkey that corresponds to the network adapter that is connected to the network.
3. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
4. In the New Value #1 box, type DhcpConnEnableBcastFlagToggle, and then press ENTER.
5. Right-click DhcpConnEnableBcastFlagToggle, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. Close Registry Editor.