I think at the time I was using XP and Vista, and I had configured Vista to disable NTLMv2 responses for an even older NAS, I didn't realize that I was fixing something on this box as well. 
Well Actualy I've been runnign Windows 7 64bit Ultimate since I got the DNS-323 (RC1, now on Retail)
and my PC and Windows XP Pro SP3 on an other one.
And I know that on firmware v1.06 I was able to access "All users" shared folder without needing to enter any credentials. And it would even show up in "Network" (win7) and "My Network Places" (WinXP)
Now (v1.08) if the Windows user that is logged in is not in the DNS-323 user list... it will NOT show up in Network... but I can still access it by entering the IP address (\\192.168.1.200)
And I also checked my default entry for "Network Security: LAN Manager Authentication Level "
And it his at its default value of "Not Defined"...
And this is from a Clean install of Windows 7 Ultimate 64bit from a retail CD