I have a four machine network. Two laptops running Windows XP Pro SP2.
One laptop running Vista Home Basic. One laptop running Visa Home
Premium. Both the Vista machines are up-to-date using Windows update.
The machine which runs Vista Home Premium is on almost all the time -
sleeping at night and being woken up in the morning. The other three
log in for a few hours daily.

The modem/router is a brand new Netgear DG834GT, firmware version
1.02.19. The Vista machines each have Atheros AR5007EG wireless
adapters, both running with the very latest driver dated 5 Sep 2009.
The network name is "Netgear". All machines are configured to obtain
IP addresses from the router, which has the correct address range
settings (i.e. excluding its own address).

The two XP machines never have any problems at all in connecting to
the network and gaining local and internet access. Ever. Connection is
foolproof and works every single time.

The Vista Home Premium machine rarely has problems. Although
intermittently, if the connection drops for any reason, the
"Indentifying network" condition crops up. Eventually it will connect
to an "Unidentified network (Netgear)" saying it has local access
only. However it has no access at all to the network and is completely
isolated. No networked machines - including my NAS and network
printer - appear and I am unable to even access the router via its
web interface. The only solution in this instance is to power the
router off and on again after a short wait. The laptop can then access
the network and the internet.

The Vista Home Basic machine has massive difficulties. But they are
intermittent and appear utterly arbitrary. The situation is
complicated by the fact that it's an Amilo Li 2727 which has a WLAN-ON
switch which will not appear until Vista has completed loading and has
already established that the machine has no connectivity. Once the
WLAN has been switched on, one of two things happens - and what
happens seems completely arbitrary:

1. The machine identifies and connects to the network correctly with
local access only. Ipconfig shows a correct 192.xxx IP address has
been assigned, not a 169.xxx address. Local machines and the NAS and
network printer are available. The router can be accessed via its web
interface. A "Repair and Diagnose" then gives internet connectivity
within seconds.

2. The machine sits for several minutes "Identifying network". It then
says it is connected to "Unidentified network (Netgear)" and has local
access only. In fact it has no connectivity at all. No networked
machines - including the NAS and network printer - appear and I can't
access the router via its web interface. There seems to be no solution
to this. "Repair and Diagnose " suggests re-enabling the ethernet
card! Rebooting makes no difference. Rebooting the router first, and
then restarting the laptop mostly makes no difference. At some point -
which it decides for itself, without me having changed ANYTHING -
Vista will decide it is happy and will occasionally allow full
connectivity.

Today, a series of 11 successive starts brought up (1) above. The
next 6 or 7 starts brought up (2) above. Then one single start came
up with (1) before reverting to (2) for successive restarts. The
problem is totally arbitrary. Sometimes it works, mostly it doesn't,
when absolutely nothing has been changed in the interim.

I have applied the MSKB published fixes.
I have switched off IPv6
All machines have their ethernet LAN adapters disabled in Device
Manager - only the wireless adapter is enabled.
I have ensured that all machines are obtaining IP addresses etc
automatically from the router.
None of the machines has a software firewall, as they all rely on the
hardware firewall in the router for their protection
Both Vista machines (which came with Norton demos) have had the Norton
Uninstaller applied.
The router is not applying MAC address filtering.

I am at my wits end with this, as the error conditions simply aren't
repeatable or consistent. One minute it will do it right, then for the
next half hour it fails.

Can anyone at all give me any idea why Vista is behaving in such an
arbitrary manner?

Is the solution REALLY to go back to XP, which seems to have no
problems at all, and was even capable of co-existing happily with an
OSX Macintosh on the network as well? The Mac is now gone, and given
Vista's sniffy attitude, I am glad!