Is the DC2003? What OS is the machine with the share? 2k3 and XP have settings to prevent anonymous netbios access from working by default (on purpose of course). One easy way to get it to work is to change the local security policy on the machine to 1. enable the guest account, 2. force local users to authenticate as guest instead of themselves ( Sharing and Security model for local accounts). Even when the Everyone includes anonymous, anonymous is still restricted from all kinds of NetBios stuff like pipes,enumerations,etc and is generally a pain in the arse to get it to work (also on purpose I surmise). Instead of disarming half the security features, it seems safer to me make use of guest, which can authenticate properly and force non-domain users to use guest, you can also control access via the guest account that way.

-Maestr0