Unable to create folders unless using UNC path

[alanterrill]

I've just installed a NAS server running 2003 storage server. It has fixed IP and is part of a single domain. I can browse to it from another PC or server, but when I try to create a new folder or file it says "access denied" although I have full rights to the whole disc. If, however, I make a mapping like \\server\users\me, then it's quite happy to let me create a folder or copy files, with the same logon. So what's preventing me from getting access through network places?
(The other pcs are running XP and the other servers are 2000. All machines have fixed IP. I have tried enabling netbios over TCP/ip, but to no effect.)