After spending few hours trying to connect, changing all the settings in the router, restarting the router like hell, I was about to reinstall the OS on that laptop. But as I never worked on Vista, I thought google-ing a bit might reveal similar experiences. And yes, I was so right… one of the first results was stating:

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.

The simplest thing you have to do is disabling Broadcast on your wi-fi card, by setting the REG_DWORD key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID}\ DhcpConnForceBroadcastFlag to 0, where GUID is your wi-fi card ID.

Other options plus the description of the whole story is available here: http://support.microsoft.com/kb/928233/en-us

… and yes, the problem is solved in Windows 7.

Good luck!

First I thought it is something hardware. Since I had a dual-boot environment on that machine, I booted in Ubuntu and saw that I had also a gateway there and internet was working seamlessly. So it was all about Windows XP…

After lots of formus read, after reinstalling wireless card driver many times, I finally found a solution here, as
- in Windows XP SP2 some repair options were added through netsh command:

So, open a command prompt (Start->Run->type cmd):
1. Reset WINSOCK entries to installation defaults:

2. Reset TCP/IP stack to installation defaults:

3. Reboot and test.

These commands are not deleting your current network configuration, but a suggestion would be to try just the first command first.
For me it solved the problem.

Good luck!

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