Vista - Vista Home Premium Network Failure after recent Upgrade!

Hi All, I had a nice network set up allowing my Laptop and Main PC to communicate both ways and transfer Video recordings from my Main to Laptop to play on the main TV running as a PC Monitor.
Come the most recent set of Upgrades and Fixes last week I found that my network had died. Luckily I subscribe to Windows Secrets and last week they listed this Tech Net Article on DHCP.
Article ID: 928233 - Last Review: June 17, 2008 - Revision: 3.1Windows Vista cannot obtain an IP address from certain routers or from certain non-Microsoft DHCP servers

I have done this register change on both PCs. Now whereas the Laptop (connected via Wifi and Netgear DG834G Router) can see all the Shared Folders on my Main PC, the Laptop still remains invisible to my main PC! It won't ping its IP. The router knows it's there but cannot get its name. I also have an older XP machine connected to the net and that is visible to the Main PC but invisble to the laptop! The Netgear is definetly set up as DHCP server and ipconfig confirms it on both machines.
Can any wise networking guru out there suggest where I look next? It seems that both machines have additional network adaptors in the Register with IP settings which won't ping. Can I delete these safely from the Register? All machines have the same Antivirus protection (Kaspersky Internet Protection 2009) and it did all work before!

Thanks in advance for any help

What firewalls do you have running on the machines, are they blocking things ?

Kaspersky Internet Protection 2009. It was running on my main PC before the update. Its rules are the same on both machines.

have you tried disabling IPv6 on the Vista laptop network adapter?

No I'm not even sure if it is enabled. The setup on both seems to be the same, hence my puzzlement!

just a quick update. I've looked on this machine and IPv6 is selected for loading in the LA Properties but there are no values assigned for IPv6 Default Gateway or the DNS server.
It's late here so I'm only on the one machine and about to switch it off for the night!

try just to uncheck the IPv6 box and see if it does any good.

Sorry Limneos I got overwelmed at Christmas and New year with Domestic doings.
Turned off ipv6 and it made no difference. Have not been able to find any clues since. I've just downloaded wireshark last night but haven't had a chance to try it.
If I wire connect the laptop it work fine. It's only when I use the wifi link that Network Discovery seems unable to find the laptop on the net as it will not ping its IP address! I have even tried making the laptop MAC code a Trusted radio device but no dice.
I'm using the Netgear DG834G v4 which is the UK version with the most recent firmware from Netgear's site. They don't seem to have a proper help site either that allows you to pose a question!
Thanks
Paul 100