Windows 2003 Upgrade issues

I recently upgrade my primary domain controller from Windows NT 4.0 to Windows 2003. I configured it for mixed mode since I still have a NT4 server as a BDC. I have a couple of XP Pro systems that log into the domain but then can’t access files on the NT4 server. When trying to access the NT4 server they get a login screen and nothing allows them to login to that server. Also, is it possible to share printers that are attached to pc’s in the domain?