After SP2 Shares ask for login/password

My setup:
2 desktops and 1 laptop
All running XP HOME Edition

Desktop 1 is a Gateway ADSL connected thru ICS with Norton Internet Security - SP1 is installed but NOT SP2

Laptop has SP2 installed.

Desktop 2 is my main PC with SP2 installed.

My problem:
After finally managing to get SP2 installed on my main desktop, the shares I had setup (including print sharing) now pop a login dialogue box with the guest account (greyed out) that requests a password for my other PC to access it.

The shares available on my laptop are accessible by all PCs.

The shares on the Gateway PC are accessible to all PCs.

BUT, the shares on my main desktop now pop the login dialogue box when the laptop or Gateway attempt to access them (including printing) - it is completely one way.

All are connected wirelessly. Standard windows ad hoc network with 192.168.0.1 (Gateway) 255.255.255.0 subnet DHCP / fixed IP setup in the that range.

ipconfig - all the computers see each other.
net view and \\computername list the shares correctly.

I have disabled the SP2 firewall.

This all worked before SP2 on my main desktop. What's changed? H..E..L..P

Check this registry Key
HKLM>System>currentcontrolset>LSA dword value limitblankpassworduse if it is set to 1 change it to 0
This tells XP only allow blankpasswords for local login to use a blank password accross the network it needs to be set to 0