Windows 7 Home Network not connecting to Netbook Options

[AlanHo]

I am having problems connecting my Netbook computer to my home network since upgrading our two desktop computers to the retail versions of Windows 7. Previously, when running the pre-release version of Windows 7 on both computers, all was OK.

The network comprises a Virgin cable modem connected to a Netgear WGT624v3 wireless router to which is connected 3 computers.
My Windows 7 64 bit Desktop - ethernet cable connection
My wife's Windows 7 32 bit Desktop - ethernet cable connected
My Samsung Windows XP Netbook - wireless connection

The current situation is that all 3 computers can access the internet without any problems - thus proving that the wireless connection to the Netbook is OK.

The two Desktop computers are able to share files across the network via both Windows 7 Homegroup and via the Windows network.
My wife's computer is able to access the USB printers connected to my computer.
However - neither can see the Netbook and the Netbook is not able to see them. Furthermore, the Netbook cannot access the USB printers connected to my Desktop computer.

I have made sure that the computers each have different names, are using the same workgroup name, that file sharing is set up and the wireless WAP key is correct - to no avail.

If I connect the Netbook to the router by ethernet cable - both desktop computers can now see the Netbook, can access (read and write) its shared files. However, the Netbook cannot see the desktop computers and share their files - they do not appear on the network map.

I doubt that the problem is 64 bit related. It started after I installed the retail versions of Windows 7 on both Desktop computers - which of course resulted in the network being re-established semi automatically by Windows 7.

I am baffled - but have an ominous feeling I have overlooked something very basic......but what?