We have a SharePoint 2007 server setup to authenticate users using SPNEGO/GSSAPI (Windows Kerberos authentication). It works great from any browsers (IE, Safari, Firefox) on Windows XP/Vista. It works just fine from FireFox on Linux. The problem OS here seems to be OSX. It works just fine on OSX 10.5.6 in Safari and FireFox when the user has administrative rights. The problem that we're seeing is when the logged in user doesn't have administrative rights (eg, they're a normal user), the authentication fails. Both browsers will continually loop with the authentication dialog box. I'll admit my familiarity with the authentication mechanisms built into OSX is a bit limited, but I can't come up with any reason why we'd see this problem across the board. Any suggestions?