Cmd-k doesn't work with Leopard to access Win XP

Question

With 10.5.4 on an iBook I was able to get to Win XP shared files just fine. With 10.5.6 on a new Macbook I've been unable to get this to work despite having fully researched the situation with Google and having tried all the suggestions that apparently didn't work for anyone else with the problem either.
I'm using SMB account sharing (well, I'm trying anyway.) The account names and passwords are common between the Mac and the PC. Everything has the right permissions but all I can get with cmd-k (using either machine name or IP) is "Connection failed. You do not have permission to access this server."
The XP machine is listed under SHARED in the finder side bar but if I click on it says "Connection Failed" in finder. If I select "Connect As" it doesn't even ask me who "As" ought to be but just puts up the "Connection failed..." dialog box.
From this it seems that Leopard can see my XP machine but not get to anything on it that I've made shared.
The strange thing and what makes me sure this is a Leopard bug is that I have removed the XP machine from the Keychain and I still don't get any dialog asking for account and password. It just barfs up the "Connection failed..." dialog.
Can anyone tell me what to do for this? If there is a bug in 10.5.6 which makes sharing XP resources impossible how about just admitting it so I can put this machine in the closet until Leopard is fixed and quit throwing good time after bad trying to get it to work.
Thanks,
Bob

Answer 1

Problem found and fixed. I've been trying to chase it down pretty much full time for the three weeks since "Security" Update 2009-1 completely hosed Windows file sharing (SMB.) I wonder if the time is billable to Apple.
The SMB file system extension was given the wrong permissions by that "Security" update and won't load as a result. Incredible. Actually it sorta makes me wonder if they didn't intentionally close a security hole by disabling SMB file sharing cause they couldn't see how to really fix the problem. I digress.
Log in as an administrator and enable root: In /Applications/Utilities run "Directory Utility". Open the lock on the bottom left. From the Edit list, select "Enable Root User". You will be asked to create a password for becoming root (superuser.) Do NOT forget this password. I use the same one as my main administrative account. Leave the utility open.
From Utilities run "Terminal".
Enter "su" and you will be asked for the above password that will give you root (superuser) superpowers.
Enter "cd /System/Library/Extensions" to get to the directory containing the SMB file system extension.
To fix permissions enter "chmod -R g-w smbfs.kext".
To start the extension enter "kextload smbfs.kext".
Close Terminal.
For safety return to the open Directory Utility window (you may have to unlock it again) and from Edit select "Disable Root User". Exit the utility.
You should now be able to connect to any Windows shares you previously established and the fix persists across shutdowns.
Bob