2003 share to non-trusted network

I had a 2000 server share that was accessible to a non-trusted domain in a seperate forest as long as I had the same users setup on both domains. I have since moved the share to a 2003 server via Robocopy, the permissions are exactly the same, and now the shares are fine on the LAN but cannot be accessed by the non-trusted network unless I set up local accounts on the 2003 server. The Windows firewall is off, and I also cannot browse and see the other network like I could with 2000. I assume I am missing some security setting on the 2003 server but I cannot find it. Thanks for any help.